Infamous Second Son contains a graffiti tagging system — a side activity where Delsin spray-paints murals across Seattle — that doubles as foreshadowing for the Neon power acquisition. Each graffiti tag depicts stylised figures in poses that match Neon’s movement animations exactly, and several show colour schemes that match Neon’s visual palette before the power is introduced.
Sucker Punch built the tagging system as both a gameplay activity and a visual language primer. Players who completed all graffiti locations before acquiring Neon were, without knowing it, being taught how Neon would feel to use.
The graffiti also contains hidden messages that encode the coordinates of specific collectible fragments. These fragments, assembled, spell a word in Curdun Cay dialect that translates roughly to ‘what is watched cannot be seen’ — a reference to the game’s surveillance themes that no official guide acknowledges.
Second Son received criticism for its relatively short length. The tagging system demonstrates that Sucker Punch packed connective tissue into what appeared to be incidental side content.

Currently on my first run and now I have to go back and look for this. Worth the detour.
Found this by accident on my third run. Came here to understand what I was actually looking at. Great write-up.