If you really want to tell someone something, try to make it quick - the actors are trying to concentrate on signing for everyone, but they never mind a little personal story, as long as it's short. For example, when I met Andrew Barth Feldman at Dear Evan Hansen, I said, "I think you're the only other person I know who looks at the Disney World wait times when they're not at Disney World," to which he said, and I quote, "Oh, hell yeah." Sometimes, the actors themselves will start a conversation - I've had nice conversations with Gavin Creel at Waitress and Harry Hadden-Paton at My Fair Lady, and I've heard Alex Brighten is able to start a conversation from practically nothing. Most of all, be sure to thank them for such a great performance.
Just out of curiosity, what show are you seeing?
"I think that when a movie says it was 'based on a true story,' oh, it happened - just with uglier people." - Peanut Walker, Shucked