A system for mounting a sign to a post comprises an elongated channel member adapted to be mounted on a backside of a sign and a bracket adapted to be mounted to a post to which the sign is to be mounted. The bracket has a channel engaging portion adapted to be slidably engaged into the channel member on the backside of the sign. The bracket comprises an endless collar extending along a continuous closed line and adapted to be fitted over the post. The collar defines at least one transversally oriented hole in which a threaded fastener is threadably engaged with a leading end thereof projecting inwardly of the continuous endless collar for exerting a pushing action on the post in order to secure the collar on the post while at the same time drawing the channel member against the post so as to prevent relative movement between the sign and the bracket.