What can you show you are celebrating?
Birthdays
First visit
Engagement / Marriage - "Happy Ever After"
Just being there - the generic "I'm celebrating" button
Anniversaries
At Disneyworld they will normally just have people with boxes that will hand them out. The "Happily Ever After" buttons are harder to come by but ask at restaurants and your hotel; they might be hiding some....
When we had the I'm celebrating button we got a lot of photographers asking what we were celebrating. When we told them that we got engaged they would then change the regular photo's into proper engagement photos. It made it even more special for us. Once we got the "Happily Ever After" we didn't get asked as much so we swapped back to the generic buttons unless we were going to a restaurant as the HEA buttons got us really great seats.
AND THEY ARE FREE!