I think this will be a good life lesson on how the world is not perfect. Sometimes people will call you Mam or Sir, especially when it is not obvious. No one ever does that to be mean. Learning to brush it off is a better way to handle this. The button idea is fine, but a cast member might not look at it, since many guests wear buttons. It is important to learn how to deal with this and 14 is old enough. I know that as a parent, we want an our children's life to be easy and happy. The world is neither. I would talk to your child about what they think and how they want to handle it. It is not worth ruining a vacation over being called a princess.
Any time we take our kids anywhere, we always go over Plan A and Plan B, sometimes Plan C, too. In other words, we let them know what we'll do to try to have our day or trip or visit go in all the ways we'd most like, but we also point out that things rarely all go exactly as you wish, and here are some of the ways we can deal with that. And that's exactly how I took the original post.
I don't see the OP saying the vacation would be ruined. They just want to try to make something more easily apparent to the CMs they come across. Last time they didn't do anything to make things more easily understood by the CMS, and this time they'd like to up their odds a bit. Just like everyone else who wears a button of any kind to a Disney park.

I'm sure they are well aware that not every CM will notice their button, or that they may give a greeting before they can see the button..a cast is noticeable from further away than a button, I imagine.

But if last time 10 CMs gave the non-preferred greeting, and a button brings that number down to 2 or 3, then I'd say that's a positive change, and we all like to find ways to make each new experience a more positive one.
