I agree with Shambles. At worst, they are looking for their 3 minutes of stardom, or the chance of a gig, or to promote the latest CD they put together. I am not concerned with floorsingers' motives, they are all valid in my book. In a singaround, everyone deserves a go.

And if your singaround attracts lesser-quality singers (by whatever judgement), don't moan about it, do something to improve it. Coach them to become better (I have seen several floorsingers flourish in the last 5 years alone, to the point where they now command gigs on their own merit - heck, I was one); show your approval of the better ones, to encourage them to come back; seed the session with some good singers that you know, by asking them to come along.

It is not enough to simply stick a board outside the pub saying "folkies welcome" and expect the rest to happen by itself. Did you get someone who knows his stuff to run the session? Did you ask them to contact some of their friends to make the session good? And did you think that the sign itself could be actually offensive, as it marginalises folk music lovers? It's like saying "dogs welcome". Know your customers before you despair of them or their absence.