It’s a caret indicator, also known as a ‘meter indicator’ or ‘meter movement’, used in navigation devices and on slide rules to indicate two states - a ‘value’ and a ‘register’, where the register state is indicated inside the box, and the value by whatever the arrow edge is pointing to. In a slide rule application, two independently movable bars are contained within the area of the symbol, with the pointer side used to select values on a scale, and the register ‘box’ side showing the results according to slide bar positioning.

It is also commonly used in compass devices to indicate a direction/bearing set by the user as a waypoint, and in digital navigation systems common at the time, would often be used in combination with the filled-in version to indicate course accuracy - when filled, the navigator is on-course, when emptied, a correction must be made.

There are also archaic physical versions of this symbol in the form of paper clips which can slide along the edge of a form, indicating the next step of a form for a department or staff member to be working on.

It was also used to indicate end of line positions in IBM typewriters, as mentioned by others in this thread.

So, a general purpose cursor/caret indicator…