I had to look this up, too.
According to the links I followed, at a con recently, some people were discussing what it would be like to just ask to touch other (clothed) people, mainly women, mainly breasts. Some people agreed, it expanded beyond the hallway where it originated. People were asked if they could be touched, they either agreed to declined. Apparently no one was pressured and all clothes remained on.

The Ferret (man on whose blog I found this info) said it was sexual but felt clean and beautiful, not 'dirty". He refers to it as the Open Source Boob project. Much of the asking was by women.

By a later con, red and green buttons were instituted, but not widely prevalent.