(covers information from several alternate timelines)
A neon sign advertising beer
A neon sign was an electrified, luminous tube light that contained neon or, sometimes, other gases.
Some bars on Earth during the 20th and 21st centuries sometimes had neon lights on their walls which were used to advertise various alcoholic beverages. In 1957, Pine Tree Bar and Grill in Carbon Creek, Pennsylvania, was one such example. (ENT: "Carbon Creek")
A neon sign was used in 2004 to advertise a cafe in an apartment block in Detroit, Michigan. (ENT: "Carpenter Street")
In the mid-23rd century, in an alternate reality, the Shipyard Bar in Iowa had neon lights both inside and outside the building. (Star Trek)
In 2384, Jankom Pog often played a street fighting sim on the holodeck of the USS Protostar. It featured alleys lit-up by neon signs. (PRO: "Ghost in the Machine")