Darley siren factory. This "helmet" siren is definitely not a Model 2. All of their siren models were called Champion, and on the 2 Hp. siren this man is building, the motor sits on top of the stator. That protrusion on top of the motor accommodates the lifting eye, while the siren rests on the base of the stator (which is visible on the completed siren in the background, painted black). There is one of these in my county, where you can clearly see underneath the siren into the rotor. I believe that Darley originally built their own sirens, but later began rebadging Federal sirens. Today they buy from Sentry, as does Edwards. By the way, "helmet siren" was my name for them because the top is reminiscent of a WWI doughboy helmet.
Regarding GCS (General City Services), they were headquartered in Minneapolis and, as far as I know, were just rebadged Federals with their own housings. I once owned a GCS Model 2 that was identical to the Federal, except that the badges on the housing and on the motor were for GCS. There may be a possible connection with the old Erick company of Minneapolis, which died out during the Great Depression, but Decot may have acquired some of Erick's materials also.
Lex orandi, lex credendi, lex vivendi.