One piece of advice. If he doesn't come through this year, tell him it hurt you. Don't sit on that resentment. It festers and grows with other things that will happen. Sometimes men are dunces and they just don't get it on their own. 

StepMother's Day is the Sunday following Mother's Day.  Bring it up to your partner and tell him that going forward, you would like to be acknowledged on that day for everything you do as a stepparent. Leave Mother's Day and Father's Day to the bio-parents and treat SM's Day as a holiday just for you! 

I have only once been acknowledged on Mother's Day as a stepmom. BM actually helped SS pick out a card. This was years ago and BM was trying to buddy up to me for manipulation purposes. Beyond that, BM has made it clear that I am no Mother figure to SS at all. And frankly, I don't want to be his Mother or be acknowledged as such. I actually prefer to not be acknowledged on StepMother's Day either. I saved Mother's Day for my DD15mos and now I celebrate that with her. 

I know it can be hurtful to not feel acknowledged for everything you do as a stepparent, which is why I think StepMother's Day might be a great option for you! 

Save yourself some grief. While you are doing "motherly" things, you are NOT their mother....as all of us here have learned over the years. There are a few families that can truly blend.....but it is rare. Think of yourself more as a friend or aunt for these girls.

I'm sorry your SO is "blind" and doesn't encourage his girls to honor you on Mother's Day for all you do for them.....many of us here have DHs that do the same thing. If you are inclined, talk with your SO but don't be surprised if he says something like "you aren't their mom" (as I was told by DHs kids themselves). If you are bothered by this, then let your SO take over all those "kid jobs" you do because in reality, it's HIS job to do those things. You can help but it should be minimal.

Your sks are young.  You have many more years ahead of you.  Teach them and teach DH how you want to be treated.  It's not unreasonable to want to be appreciated for your role in their lives.  If DH doesn't want to do it for Mother's Day (as the previous poster suggested), then tell him you expect to be honoured on Step Mother's Day (the following weekend). If he doesn't have a strong objection, pick the day you want more.

DH likely won't realize it means a lot to you.  Additionally, part of raising kids is teaching them empathy and gratitude.  For all you do, you'd like to be honoured.  DH needs to take the lead to ensure it happens, and then you need to genuinely ooooh and ahhh and fuss over how much it means to you.  That positive feedback will teach them empathy.  But realize that next year, they'll likely forget again.  Remind them again (a week ahead of time!).  Eventually they will remember on their own.

Don't hint, don't take offense - communicate directly with DH.  Tell him you want breakfast in bed.  Or a hand drawn card.  Or flowers presented by each of them.  Whatever is appropriate for Father's Day - teach them that the same amount of energy/effort is appropriate for you (assuming you really do act as a Mom to them.  If you're generally disengaged all of the above is moot.  You're looking for acknowledgement in line with the effort you give).

I forget birthdays.  My siblings and I remind each other.  I'd rather have clear communication that wallow in hurt feelings. 

Since they are 9, this is all on your DH. I would do like the above poster said and remind him (sweetly) when Stepmother's Day is. If he wants you to keep doing motherly things, he should show some appreciation. 

"Honey did you know the Sunday after Mother's Day is Step-Mother's Day?"

This is tricky. If the bio mom is not a great mom, I would bet any money that she would go ballistic if she found out that "her babies" were celebrating any other woman on mother's day. Your stepdaughters could get a lot of crap from their mom which would create a loyalty bind.

All the things you do, you really do to help support your partner, and he should be the driver for showing appreciation for you on mother's day. If he says, "Well, you aren't their mother" tell him "That's right! So that means that I can kick back and leave all the parenting to you including help with homework, rides, hair brushing, lunch making, etc. Thanks babe. I'll remember my place."

I would ask DH what kind of relationship he wants years from now and how he expects you all to get along.  If he has some fantasy answer and is not on track for that to happen, read him stories from the adult forum.  The really bad ones.  It is up to HIM to teach the girls to respect you, the things you do for them and to do his upmost to make sure they understand and respect your role in their life.  If he wants a happy life in the long run, he puts the effort in NOW to make that happen.  
 

I wouldn't hesitate one second to go on strike if he forgets you.  If they forget you.  I don't think it's too much to ask.  It's also necessary to point out the obvious to men. They are simple creatures at times. 

Expectations from children who already have a mother to include you on Mothers Day seem a bit presumptuous

I dont think you should expect anything from them. Maybe they will get you something or remember you as some sort of "maternal figure' but I highly doubt that. Prepare to be disappointed if you have these expectations

My SDs only acknowledged Mother's Day once for me. The first year I'd been around. And DH instigated it. But they obviously loved doing it. After that NADA - then began the second year of being yelled at "You're not my mom!" and my disengagement started out. Slowly, but it started.

I have to give DH credit. He asked me how I felt about Mother's Day and I told him I'm not the mom, I don't want to be the mom or function like their mom and they reject it so forget about it. And that's been ok with me. They didn't even ever acknowledge my birthday (often DH didn't even have them on that weekend which was great in my book).

I would immediately discuss it with your DH and I like the suggestion of Step-Mother day; you do more than I was doing after three years so you should receive some acknowledgement if it's important to you. He gets father's day right?

Something I learned in Al Anon:

Stop having expectations, they are a recipe for disappointment and resentment.

If you do someone a favor, or give someone a gift, or a loan, etc, assume they will not reciprocate or thank you or repay you. Knowing that is a possibility, only do what you want to do, only give what you want to give, freely, without expectations, without resentment.

You are not obligated to do anything for these kids. Everything you do for them is a gift/favor. Remember that.

But it's also a good idea for your DH to teach his children about kindness and gratitude, so maybe mention it to him and then let it go.

I've been with DH for 4 years. We just got married in January this year. SD10 has never, not once, acknowledged me on Mother's Day and that's been fine with me. I wasn't really apart of her day to day life until about the last year. We mostly spent time together on weekends, holiday breaks, etc. before I moved in. So, I really didn't expect anything at all. SD didn't really even start acknowledging me as her stepmom until after I moved in anyway. I've helped her pick out stuff for BM in the past, and we've made crafts for her, too, but I've never really pushed the idea SD should do anything for me... until this year. DH, SD, and myself were all at the table earlier this week and DH said that SD should start thinking about stuff to make BM for Mother's Day and I said, "And you know, Stepmother's Day is the Sunday after so..." and DH said, "ooh yeah! You better think about that, too, SD." And honestly, that's all I'm going to say about it. If DH and SD decide to do something for me, then that would be wonderful, but if they don't, I won't be surprised and I'll let DH know about how I feel. I've learned the key is low expectations. Sometimes we're treated like a guest star in our skids lives and that hella sucks. Especially when we work hard to make their lunches, play chauffer, and encourage them to be good people. Trust me, there are times I cry in my bedroom and just think, "This is such a thankless waste of time," and then I remember all the good my stepparents have done for me and hope one day SD can say the same. Maybe one day there will be flowers and a card for me on Mother's Day, or Stepmother's Day, but this year the bar is basically on the floor. Even just saying, "Happy Mother's/Stepmother's Day" would be enough for me. All we want is to be acknowledged for the sacrifices we've made for our stepkids. Personally, every year on Father's Day, my stepdad gets a card and a few new button up shirts from me that he wears until they are threadbare, lol. My stepdad is my dad but it took a long time for that to happen. Be patient, set your expectations, and make sure your partner knows when they aren't met. 

about recognition as a father to my SS-30. I am the first person he ever called Dad(dy), I am the dad he has early full time memories of, he asked me to adopt him and wears our famly name on his USAF uniform. When the adoption was signed when he was 22, 4 days after he asked for me to adopt him, he and his mom shared a last name for the first time.

I have always been his dad.  Even  before his mom and I married the week before he turned 2yo.

He does not always send me a card, in fact he rarely does. But he does call me for every FD though some years it a day or two early, other years it is a day or two after and even other years it is on FD.

I get how being the only REAL mom or REAL dad a SKid has and not getting some recognition can be angering.  

For damned sure your SO should be recognizing you whehter your Skid's do it.