Short for Significant Other; siggos (plural)
Margaret: We are all going out for drinks tonight, you should come, bring your siggo.
Slang for 'Sig'nificant 'O'ther .. Used to describe one's boyfriend, girlfriend, husband, wife, lover, Life partner etc.
We're meeting Kurt and his Siggo later for drinks at the Triangle.
Qdoba is offering buy one get one free entrees on Valentine's day, if you kiss your siggo when checking out at the register.