How is tagging commonly defined in the context of gangs?

Tagging is commonly defined as illegally scribbled or sprayed markings, which is a prominent activity associated with gang culture. This form of graffiti serves multiple purposes: it can signal territory, show allegiance to a particular gang, or communicate messages among gang members. Tagging often involves the use of spray paint or markers to create stylized signatures, symbols, or artwork in public spaces. This not only establishes a gang's presence but can also convey challenges to rival gangs or commemorate events relevant to the gang's history or identity.

The other options do not align with the established practices typical of gang activities. For instance, formal invitations and official gang contracts suggest a level of organization and legality that contradicts the often illicit and spontaneous nature of tagging. Secret codes may play a role in gang communication but do not directly relate to the visual and public marking associated with tagging.