Personally, I don't see why there would be a need to add anything like that. If someone doesn't remember their own anniversary, it isn't a big deal. Besides, unless they're insanely popular people around here, not many members are really going to care about someone's anniversary for whatever it is they're celebrating. Like Derozio said.
I know I generally don't care if someone joined a year ago, to be quite honest. May 7th isn't exactly a date I mark on my calender, either. The only reason I remember it is because it's two days before my birthday. I remember getting a celebration for my one year anniversary and then not getting one for my birthday. Don't think I replied to my anniversary thread, either. Didn't matter much to me back then, or now. But that's just me... even though I think I speak for a good part of the community when I say that.
Not to be rude or harsh or beat down your suggestion or anything, just my opinion.