You can get a birthday button at guest relations at the parks. While not guaranteed to get you anything per se, it does seem to bring out something. As long as you're not expecting it at every turn just because you wear a button, you'll be pleasantly suprised.
My son wore it one time and he got a birthday cake at CRT for lunch one day, and an free scoop of ice cream at another place. The birthday button gave him extra notice from the CMs, like the Barbershop Quartet singing especially for him, and CMs coming up and saying happy birthday to him, etc.