A $250 reward is being offered for information about people posting graffiti on public or private property.
Police believe a new gang is "attempting to expand its influence in the area and is recruiting young people."
Graffiti is posted usually to claim or mark territory, issue challenges and warnings or gain notoriety, the release said.
Police are asking the public to report any new graffiti that appears in their neighborhood and to report any suspicious activity.
If you see suspicious activity happening, call 9-1-1. For other reports, call 360-740-1105.