Someone sent me this photo of a device and is asking what it is. Can anyone identify it?

It's a "block instrument," as used in British signaling practice. Check for websites explaining UK signal practice to get the whole story.

There probably is bell on the block indicator. Until very recently, telephones were not considered primary signaling equipment. Block occupancy is coordinated between each signal box and until recently, the bell was the preferred form of communication between signal boxes. They have a bell code for every type of train (even Eurostar) and situation. Look up signal box on YouTube and listen to the operators "talk" with the bell signals.

Unlike most US tourist/historic railways, many heritage railways in the UK are signalled and employ signalmen as most signal boxes on those lines retained their manual signals and points. Also, at many locations, the signal box controls the pedestrian and carriageway crossings and the signalman is responsible for opening and closing the gates.

I looks a bit like a "staff" dispenser. A variety of Automatic block control (systems were offered by Union Switch & Signal)

If you had the staff (a stick reported as either 6” or 20” long) then you owned the track. At the end of the block you returned your staff to a dispenser, clearing that block. There would have been two dispensers, one at each end of the control block, connected via telegraph… Each held a number of staffs, but they would only dispense one if the block was clear. With several staffs available at each end you could have multiple trains going the same direction.

Central Pacific used a staff system over Donner Pass for several years starting in 1905. John Signor describes the system in his book “Donner Pass”

Randy

I think this is what you're referring to. These were also connected via signal bell and electric plunger (to release the staff or token). Also, the staff or token had the section stamped or engraved on it so that there was no confusion as to what section the engineman had the right to occupy. The staff or token instrument was only operated by authorized employees (usually the signalman) to prevent errors from occuring. In Britain, there was a deadly head on collision where an unauthorized station employee operated the staff machine and thinking he had obtained the staff for the section ahead, handed the staff for the section that the train had cleared back to the driver, who failed to examine the staff.

Also, the staff could (and often was) used as a key to unlock ground frames within the section.