I've had that happen to me a lot. (Not as often here in Dallas, TX... as it did in Rochester, NY.)
Does it bother me? It depends.
If it's at a nice restaurant, then it's not polite to bother a couple sitting at a table. If you absolutely have to bother them, then make sure it's short and simple. We've had friends see my wife and I while they're walking in/out. So, they will stop and say "hi" before exchanging a few words and then move on. We're fine with that. We don't like it if they stop and spend the next 15 minutes chatting away while our food gets cold.
If it's at a fast food restaurant, at a mall, or at a store... then anyone can bother us.
Now, signing skills... that's another story. We don't mind someone who is learning ASL to try to communicate with us. We can understand them if they talk normally or sign awkwardly, but not if they're going to stand there trying to sign every... single... thing... SLOWLY! Argh!
There was a time when my wife and I were eating dinner at a nice restaurant. Some guy approached us and told us that he took an ASL class years ago, but forgot most of it. Then he proceeded to introduce himself... in sign language... awkwardly.
HELLO... *looks up* MY... *looks around* NAME... *hums* IS... *looks constipated* M... S... *looks at hand* *shakes head* "Sorry. My bad." *slaps hand* A... R... P... *shakes head* "Boy, this is tough!" *slaps hand* K...
So, it took him 5 minutes to say... "Hello, my name is Mark."
He then tried to continue the conversation, but we interrupted him by telling him that it was nice see that he remembered some sign language and that it was nice meeting him... then wave down our server to ask for a refill. (HINT! LEAVE US ALONE!)