I've never been able to decide if those type of people are absolutely oblivious to what's happening or if it's a subconscious ploy to get attention drawn to themselves.

And, they always seem to go to the person who is singing or playing the lead at the moment, never to who is playing backup.

In your case, Kim, it sounds like it was one of life's little dilemnas - ignore the person, or hand out a card and get more work later !!

I've been tempted to make a big production of it when one of these people interupt - saying "Well now folks, we're happy to have with us today one of the finest pickers and singers in this part of the country, old Joe Blow," and as you're saying this you hang your banjo or guitar around their neck or hand them your fiddle, and then say, "And which one of your tunes are you going to bless us with today?"   Of course it could all go horribly wrong - they could break an instrument, or worse, be a truly gifted picker or singer. But, in fantasy land it's fun to imagine. :)