The Thieves Cant is a highly specialized code for putting messages in seemingly plain speech. Also included in the Thieves Cant is a select group of symbols that mean certain things, unnoticeable by the regular person.
Guild: Denoting the building or person nearby is part of the Guild.
Safe: Denoting the area is safe for the Guild.
Danger: Denoting someone nearby or inside does not take kindly to the Guild.
Escape: Denoting that following this mark leads to escape (usually from a jail cell).
Protected: Denoting the area or people are under Guild protection.
Fence: Denoting there lies a fence inside.
Cache: Denoting a Thieves Cache
Loot: Denoting valuables or riches lie inside or nearby.
Empty: Denoting there is nothing of value inside and has already been looked over.