This interesting cryptic originated in the Southern Iowa town of Ottumwa around 2004-2005 (approximately).
The secretive digit and letters were displayed on the t-shirts of a few dozen male students of the community's high school. Many of the local residents saw this as an indication that the combination represented a club, team, or gang's, logo.
The first editions featured a black shirt with red lettering. The group was overlooked by many and little amounted from this prelude. In the Spring of 2005, a new style was introduced by the group. The new style flaunted a blue shirt with white lettering and two new features: personalized numbering similar to a jersey and a quote across the scapula which read "BAD is the new GOOD."
This edition created a rather widespread curiosity and controversy; however, the group remained silent as to what the symbol represented. Many people created speculations, opinions, and hypotheses; however the group was determined to let the public's imagination wonder.
In the Fall of 2006 a prior member of the group (who wishes to remain anonymous) released the definition of the conundrum. According to the previous member, 6KR stands for 641Krew.
Explicitly, it designates each member of the group as a member of the "Crew" from area code 641. The members intended for this to be what females would remember as the "Crew" prowled other towns, regions, area codes, etc.
Female 1: "Hey, did you see that guy?"
Female 2: "Yeah I did, he's hot!"
Female 1: "He looks like a basketball player."
Female 2: "I know! I recognize him from the Wizards!"
Female 1: "That's right! Did you see the 'Game of the Century' last night when they owned the 6KR guys?"
Female 2: "Oh yeah, the showed those jerks what's up..."