we used
If you're going to go Greek.... why not be a Goddess?"
(sorority letters)
and
our letters inside the hot wheels logo on the front of the shirt and "too hot to handle" on the back.
another house on our campus used,
"Playmate of the Year" with the playboy bunny logo on the back of their shirt with their letters on the front.
this house also used, "Absolut ABC" (on front) and then named the top 10 reasons to join their house on the back. (their #1 reason, that goes with their letters, "everyone wants a piece of the pi").
hope these help you out a bit. i'll try to think of a few more.
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