Years ago, I used to go on field trips in a convoy of vehicles with a group of radio amateurs and we used 2M (146MHz) TXs into 5/8 whip antennas on the vehicle roofs and attached to their tip were NE2 neon indicators which would glow whenever the TX was keyed on.

At night the neon glow seemed to hover above the vehicles as if suspended in mid air (it was difficult to see the antenna in the dark). A light suddenly appearing out of nowhere used bemuse other motorists. Trouble was it also attracted the cops although they never took any punitive action.