It is popular for fraternities to steal stuff from other fraternities. By steal stuff – I mean take fraternity memorabilia from another chapter, not steal computers like Jeremiah “Holy Moly” Masoli. Most of the time, the fraternity that steals the stuff does not have the intention of taking and keeping the stuff forever. They are simply borrowing it for a while in the spirit of a good rivalry.
I strongly encourage your fraternity to not participate in this type of discourse. Every time something is taken, it creates a hostile environment between the two fraternities, even if the prank is not malicious in nature.
For example, my fraternity was planning on taking a road trip with a sister chapter of our fraternity at a neighboring school. A few nights before the trip, our fraternity president borrowed a symbol from the sister fraternities pledge program. The plan was to give it back during the road trip. However, our president never got the opportunity. The sister fraternity was so pissed, they decided not to come and that essentially ended the relationship between the two chapters.
This example is a best-case scenario of what could happen. Every fraternity brother knows of instances where a fraternity has vandalized property to get back at another fraternity. The joke will never have the good-natured spirit the stealer anticipates. That is because 20 year-old guys are not capable of thinking that rationally.
Long story short – stealing from other fraternities is just not worth it.