Lots of differing opinions here so here's my two cents. If your birthday is within a week or two of your trip and you want to celebrate by wearing a button, go for it. If it is beyond that, ask yourself if you would still wear the button if it included your actual birth date. Would you wear a button in November that says "Celebrating my May 10 birthday"? How do you think people would react then? Would you wear mouse bridal ears years after you actually got married? There's certainly nothing wrong with doing what you want to do, but wearing a button is an open invitation to getting attention from others. You want the attention, go for it. By the way, what do you say if someone asks you when your birthday (or anniversary, etc.) actually is? Do you 'fess up?