US&S H-5 Dwarf, off the Milw Road. Probably off a signal bridge.

For a change of pace, I replaced the green lens in the mechanism with a blue one, so I can blue-flag vehicles in the driveway :-)
More shots of the H-5. Note the closeup prism in the middle of the lens.
Cutaway of the H5 from Union Switch & Signal. (RCT&HS Collection)