Knickname for Sigma Nu fraternity. Used in a completely endearing way. Also referred to as Sigma Who? and Snu's. Sigma Boo on Halloween.

You won't get raped at their parties.
Girl #1: Those guys are so cool, what frat are they in?
Girl #2: Oh, they're my Sigma Poo's!
by Snuforeverrrr January 17, 2012
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