As far as the Decot theory goes, they look very similar to photos of known Decots being installed in Seattle in 1951:
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I believe these sirens are Federal Model 5 and the Ports are 10/12 The ports so not look like decot's ports which were more higher and narrow. Besides the son of Ted Decot kept the patent rights on the decot design to this day. Only one person has permission to make a decot siren