https://www.google.com/maps/@38.8671813 ... FQAw%3D%3D
As you can see, there's a Fedelcode 5/7 on the left; at least that's what I think it is, although it appears to be on an STH-10 mount/base. The department was organized in 1942, so this siren is consistent with that time. Perhaps it's an STH-10 underneath though, and the housing is from the original siren?
But what really confuses me is you'll notice there's another pole to the right that clearly had a siren on it at one time. It even still has the mount and control box. A couple of people have told me it looks ACA, and have suggested it could have been a WAWAS Allertor location. To my knowledge, there were no WAWAS sirens in Fauquier County, although it's certainly possible due to its proximity to DC. Their poles were usually much taller than this, but who knows...