Carl Johnson has to search for a total of 100 gang tags all around Los Santos and spray over them with the Grove Street Families' emblem with a Spray Can. A tag needs at least 29 units of spray can "ammo" to be completely sprayed over. Tags and their basics are first introduced during the mission Tagging Up Turf. Spraying over an enemy tag increases the player's respect and respraying all 100 tags is required for 100% completion.
Upon completing all the gang tags, the player will receive certain rewards. These are:
If the police spot Carl spraying a tag, a wanted level will be applied, which should be noted with tags located in high-traffic areas. This is because the spray can is counted as a weapon, and "firing" a weapon will grant CJ a wanted star when caught spraying, though a "real-world" perspective can also be applied in that spraying graffiti is generally considered an illegal act by itself as vandalism.
A tag is not considered sprayed until the on-screen message appears and confirmation sound is played, which can be triggered without the tag being completely covered and so can still be locked on.
Spraying over any tags that will be used in the mission Tagging Up Turf before the mission will result in the tag being reset and requires respraying every tag in that mission again.
Before Carl unlocks the spray can item in the Johnson House, he can find one on the rooftop of the shop directly behind the house, which can be obtained by jumping onto the low wall in the alley between the Johnson House and Ryder's House.
The Varrios Los Aztecas gang tag is orange (like the Vagos), however, their gang color is turquoise in the beta.
From the start of the game up until Sweet's arrest in The Green Sabre, the Temple area is territory of the Temple Drive Families. It is only after that mission that Temple gets occupied by the Ballas, so it must have been a mistake as to why 'Temple Drive Ballas' tags are present right at the beginning.
Spraying all the tags won't reward the player a lot of respect, despite the game telling that spraying a tag will gain CJ respect in the mission Tagging Up Turf.
Some of the well hidden, out-of-sight locations of the gang tags make no sense from a realism point of view. Gang tags are supposed to warn rival gangs, unwitting pedestrians and cops of the gang's presence; as a means of 'marking one's territory'. They do however, make some sense as a gameplay element to denote a 'hidden' collectible and a secondary challenge.
Tags are the only collectibles in the game that are 100 in number, whereas all other collectibles are only 50.
Permanent textures of gang markings, usually done in black paint, can be found all over Los Santos. The player cannot manipulate these in any way.
In the second official trailer for the game, a Kilo Tray Ballas tag is shown in a bright red colour instead of purple.