This achievement is earned for finding optional graffiti #4. If missed on the first run, you can choose the episode from the main menu and select "Collector Mode
". Now, you can use a scene select option to browse the locations and choose the area you need.
The following collectible can be found when changing clothes inside the small cement block building. Before exiting the area, make sure to draw on the wall.
] - Optional Graffiti #4