Having re-read this thread a few times, it seems to me that the whole subject of "Display of Symbols" should be addressed not by individual chapters or schools but by each national fraternity organization. Better yet, perhaps the Inter-Fraternity councils or National Pan-Hellenic could come up with one set guideline to be followed by all?
To clarify my previous post, we also had mixer t-shirts and sweatshirts for football etc...and that was viewed differently. If you were a girl wearing the shirt, you belonged to the sorority on your shirt and vice a versa for the fraternity. If you tried to get away with wearing letters that weren't your own, folks knew it and called you out for it big time especially at a party. Hey, you didn't pay for the beer and food after all.