A term commonly use to describe the bandana that gang bangers, gangsters, kids influenced by rap and others wear in their back left pocket to signify allegiance to something. Members of the Bloods wear red flags whilst Crips wear blue flags. These can be found in the back left pocket, around the head, neck or wrist. Others can wear them as a sign of support towards friends or a particular ideal.
"Saw him rockin' his red flag in his back pocket"