Kris,
I don't know about protecting your letters, etc... but--
http://www-scf.usc.edu/~zetasphi/zeta.htm
that is the USC chapter's website, they claim to be the alpha chapter, why not start with a letter informing them that they are NOT the Alpha chapter...
Greek Life at USC is very centered on NPC/NPHC/IFC GLOs, so my guess is Zeta Sigma Phi at USC is either a MCGLO or a very small local club.
Amy