PRR two-position mechanical semaphore signal
The blade drops to vertical to display the "clear" indication when the cable is pulled slightly. The blade returns to horizontal (to display "stop") via the counterweight when the lever controlling this signal is returned to normal.
This signal was built from drawings and photographs found in a US&S co catalog from the turn of the century. It is part of my project to build a functioning mechanical interlocking out of lego.