Never use Wikipedia as a source. According to the OED, it means either Government or General Issue, and originates in the 1930s. 'Nuff said.

I have to laugh at the douches talking about their own IQ scores (asking us to take their word for it), or those slamming members of Mensa because there are other organizations which require a higher score. Triple 9 by no means is the hardest to get into anyway.