I am so one of those people who try to grab rare characters whenever I go to the parks. 

However, just to clarify, the WDW characters are not trained in a formal sign language.  They are mainly pantomiming and gestering (which is more universal than, say ASL).  They are more than happy for you to talk to them, just know that they talk back in their own Disney way.

I noticed that someone who was playing Dale used the sign for beautiful. This is not what you would think of when you are playing charades.

Well its not what I would use.

I’m sure everyone is different, but they do sem to love it when you understand their gestures/ signing.