I also suggest we start man-ing up and politely inform for these folks that they need to include folks waiting behind them or move on. The headphones are just a hog tactic so no one asks them to move. Some dudes (and it's always dudes) just pretend they can't hear ya. I know I have been too chicken to do it and I just start being passive aggressive about it. I get bummed and the hog keeps hoggin'. More than once I have seen this type of rule posted and then ignored at shows. It's our responsibility to create the proper folkways and morays expected at these shows. I think this sign on the machine is a great idea so that you can just point at it for Mr Headphones to read.