Why those letters? (public/private)

[naraht]

After talking for a while on the Philippines GLO bulletin boards, I've come to realize that somewhere near half of those groups have *obvious* places that their choice of letters come from. For example. A group called Triskelion Grand Fraternity is Tau Gamma Phi (and their Sorority is Tau Gamma Sigma) and the "Medical School Fraternity" at one school is Mu Sigma Phi. (yes, you can cry now)

OTOH, in the United States, *most* Greek Letter Organizations (used in the widest sense) have the reason for choosing those particular letters (and for most, that particular order) private to the members of the group.

The only exceptions that I'm pretty sure of are
Phi Beta Kappa (Honor)
Delta Upsilon (NIC) (I know that Dikaia Upotheke (Justice Our Foundation) was adopted 24 years after the founding, but since the fraternity is public, I presume that information is public as well)
Omega Psi Phi (NPHC)
Gamma Sigma Sigma (Service)
I've also seen some Honor Societies where the letters were chosen from those of groups that merged to make the new honor society.

Are there any other where that information is public? I'm *not* looking for secrets here, I'm looking for groups that the reason for choosing those letters could be included in a description of the group in the Fraternity/Sorority page run by the Dean of Greek Affairs at the school.
(For example for Omega Psi Phi http://students.georgiasouthern.edu/...laimer_opp.htm)