Here's a link to site shopgirl mentioned (UVA sororities) --
http://www.student.virginia.edu/~isc-uva/chapters.htm
It's pretty cool, because a lot of them have a big Z on the house, or a big IMP, or both. Does anyone know more about this? Do the tags stay there all the time, or do the houses remove them? Would the other sorority members even know who in their house is a member of either group? If your house has both Zs and IMPs, does that create problems? I'm assuming nobody knows how people get into these groups or what they do, since it's a secret, but I'm curious! It's really fascinating.