Fire alarm circuits were strung atop the poles that you see. Their mountings typically were vertically mounted pipe stanchions with standard-threaded 90-degree pipe bends with the same fittings on their short "arm" ends (facing vertically of course) that wooden pins were inserted into. At least two holes were bored through the pole-mount end; often these pipe-ends were flattened for improved "adhesion" to the pole. Many of these "pipe arm" poletop extensions were once used along the East coast for supporting early fire alarm telegraph wires. The last-known ones in the air (to at least me) were in Albany, NY as I recall in the late 1980s, having long since been disconnected but still up there.

The 10-pin crossarms beneath likely supported telephone subscriber circuits.