I'll one up this. I recently went to Kaiser for a procedure and they handed me the signature thing and said, "you need your signature to indicate that you've checked-in". So I signed it. As the final part of check-in they handed me a stack of papers and said, "here's what you signed!"
I was stunned because they never gave any indication that the signature was for some sort of contract/legal form! Perhaps I should have suspected, but it still seemed really underhanded… If they had, I would have insisted on reading it first. Luckily, reading it afterward it was something I would have signed anyway, but come on!