Hi -- I posted this under "Fraternity Rush Shirts" in the Rush forum last week. Maybe it will help you with some ideas for a shirt.
One of my all-time favorites was a PIKE rush shirt from 1993. The front of the shirt had a picture of a white cat with black spots all over him (like a dalmation) in a red circle with a red line through it. Pi K A was underneath in red and gold.
Then, on the back, was a bigger photograph of a dalmation sitting in the middle of a bunch of other white cats with black spots. Underneath it said, "In A World Full of Copycats, Be An Original."
The guys got the idea from an actual poster (I have one) that has that caption underneath. They just got the picture and had it made into shirts. It looked great!