Assuming you have the familiar Postal Telegraph clock, then it’s a Hammond clock with a standard Hammond movement. These were made in the 30’s. The movements are not made anymore, of course, but there are lots of them still in circulation.
Hammond clocks have the charming quirk that they are not self-starting. When power is applied, the rotor just hums, without rotation, until the spin-to-start knob is turned. That’s enough to start the motion and sustain it until power is removed. Hammond advertised this as a feature back in the day; the idea was that a person might have been unaware of a short-term power loss, and might therefore be unaware that his/her clock was behind. A Hammond would alert you to a power loss by staying motionless until re-set. Fair enough, but it does require taking the clock off the wall to re-set. The Postal Telegraph clocks are large enough to be unwieldy.
You could certainly retrofit a different movement to your clock, but that would kill the charm!