From Rap Dictionary
- To make a graffiti sign/signature saying this is your gangs turf.
- To steal away an area played out diss, putting your gangs sign over a rival tag.
- To go shopping. Popping tags refers to popping the tag off a new piece of clothing, more likely a shirt. It means that many rappers are popping tags, as in buying new clothes all the time, and never wearing a shirt twice. "I stay popping tags", meaning that I always buy new gear, clothes, and never wear one shirt twice, cause I'll just go buy another one. Jay-Z be poppin' tags, leavin' the mall with heavy bags -- Jay-Z featuring Big Boi, Killer Mike, Twista (Poppin' Tags) 
- When you are out shopping and you pop the price tag of one item, and change it with a cheaper price tag.