Patrol marker
From Arkham Horror Wiki
This marker is included with The Curse of the Dark Pharaoh (Revised Edition) expansion, and represents the increased vigilance of the citizens of Arkham resulting from the strange happenings which accompany the Legacy of the Pharaohs exhibit. Certain encounters will instruct that a Patrol marker be placed in a specified street area (there is never more than one Patrol marker per street area). Whenever an investigator wishes to move though or end movement in a street area with a Patrol marker, he must make a Sneak (+0) check. If the roll fails, then the investigator is arrested. All Patrol markers are removed from the board whenever the terror level increases.