Nixie Tube

A Nixie tube, is an electronic device for displaying numerals or other information using glow discharge.

The glass tube contains a wire-mesh anode and multiple cathodes, shaped like numerals or other symbols. Applying power to one cathode surrounds it with an orange glow discharge. The tube is filled with a gas at low pressure, usually mostly neon and often a little mercury or argon, in a Penning mixture.
Although it resembles a vacuum tube in appearance, its operation does not depend on thermionic emission of electrons from a heated cathode.
It is therefore called a cold-cathode