A transmission system for louver type sign wherein the signs consist of a plurality of multiple faced louvers having indicia defined thereon and the side-by-side relationship of the louvers permits pre-selected faces to define a complete image. The adjacent transmissions (10) are operated by a constantly rotating drive shaft (16) and the louvers may be simultaneously rotated or may sequentially operate in a delayed manner wherein the indicia on the louvers is progressively revealed in a "wave" manner. The drive shafts (16) of adjacent transmissions are interconnected and a plurality of transmissions are operated by a single constantly operating motor drive source, and in the disclosed embodiment, a complete rotation of the transmission's drive shaft produces one-third of a rotation of the output shafts (24) operating the louvers. A positive detent lock operated by a cam (34) formed on the drive shaft gear (22) produces a positive locking of the output shaft (24) and the position of the louvers, and the detent (38) is automatically engaged and released in the proper sequence by the cam.