Short for signature. It is someones signature thing they do or something they do a lot. Originated in Sammamish, Wa around the year 2005.
Guy 1: "Graham just said something really dumb"
Guy 2: "wow that is so sig"
by 5oul 3ater May 8, 2007
Short for "signature". Most recently used in relation to forum signature images.
Person 1: Have you been over to Allen's sig shop yet on the forums?
Person 2 (proudly): Not yet... I'm still using the sig from the last forum I was admin of.
Person 1: Dude... It's a pic of a baby in a diaper... This forum is about high-powered weaponry... Get a new sig, man.
by A. Prog. August 17, 2011
a thug ass pistol made in Germany

thug niggas like lil wayne can often be seen brandishing them
"White wife beater with the Sig underneath it"- I'm So Paid, Akon Ft. Lil Wayne & Young Jeezy
by jackson springfield67 February 9, 2009
To talk shit to someone. Origin: VALLEJO, CALIFORNIA.
That man was tryin to sig on me so I hit the fool in his mouth.
by H22CL December 22, 2005
Do you know anything about the mechanics of these old cars?
No, but I found an SIG on the internet.
by Patricia Lincoln August 9, 2007
Hey Hilary, you and the sig should really come over for a threesome.
by 101000001 August 17, 2007
The unique and/or distinctive signature one puts to be displayed every time he/she posts in a forum. Usually produced in Adobe Photoshop, it has a wide array of possibilities to be portrayed. There are many different sig styles, and entire forums are devoted only to the advancment of signature making.
*Here you go, I made this sig for you!
*Can you please rate my sig I just made?
by epic July 28, 2005