It is an Los Angeles Police Department's elite tactical detective squad with a straightforward mandate: Track down the City’s most dangerous offenders and take them off the street. S.I.S. are possibly the hardest-working, most dedicated men and women Detectives to wear a badge.
Alonzo: Yeah, S.I.S. Detective.
(from 'Training Day')
Miguel's text: "yeah i'm really excited to see you too (s.i.)"
Ted: "Of course not, he even put 'sarcasm implied' in the text! You must be really dumb"