We'd have to do a LOT of expansion before we ran into that problem!
We have:
Alpha Phi (Ohio University)
Alpha Chi (Boston University) (could be taken for AXO)
Phi Mu (SUNY Binghamton)
We too have an Epsilon Zeta chapter (ASU)... if I'd joined that chapter I think I wouldn't have gotten a chapter guard
(Some of these might be closed. I'm using AEPhi's website as my reference because I'm too lazy to get out my new member manual.)
I too wonder what you'd do if your chapter designation was the same as another sorority on campus... like if you're in the Alpha Phi chapter and Alpha Phi also has a chapter at your school. I can imagine a lot of confused PNMs...