This video , that showing the enhancer of a Philips 70W MH lamp during a hot restrike on an Osram Powertronic ballast, brought to my head the idea that enhancers can also be used as operating indicator lamps for ignitors and electronic ballasts ignition systems operation, as these enhancher lights only when the ignitor/electronic ballasts, cold or hot restriking the lamp.
This is very useful to visually indicating the operation of smart ignitors and electronic ballasts with an intervals based ignition, as the enhancher can display when the ignitor/ballast firing and when it is not by light only when the ignitor/ballast firing, and shut down when the ignitor/ballast, enters a delay.
This is also usefull to assist in detecting a faulity ignitor or ballast (Enhancher wouldn't light if the ignitor or the ballast don't works).
The enhancher can also display the behavior of the ignitor visually during the hot restrike of the lamp: With an Eltam ES-50, the enhancer would flash 4-5 times per sec. With a superimposed ignitor, it will flicker 50hz, and with an electronic ballast, it willn't flicker at all.

The "enhancer" is in fact a glow discharge lamp with one electrode direct internal and one induced external, designed to glow mainly in UV, in order to emit electrons from the main arctube's main electrodes for ignition.

As UV emitter, it's usability would be rather problematic.

But you can use virtually any glow lamp in the same arrangement:
Take any "drop style" neon indicator lamp, tie both leads together and connect to the HF source to be signalized.
In most cases it would visibly glow even without any nearby external electrode - the "ground" potential in the "infinity" would be most likely sufficient

But you could place the lamp close to metal surface HF grounded, so the current would be higher.

And you may search on Youtube for videos showing the fluorescents glowing very brightly with only one end connected - again the same concept, but not practical anymore for the purpose of HV indications...

Steinitz did sell a "HPS fixture tester" that apparently works like this
http://web.archive.org/web/20020610173901/http://www.steinitz.com/4HighBayindustrial.html#ST-723a

Such glow lamps are not only used in lighting. The most weird place i seen one was in a "storage cabinet with deodorizer" combined with a cold/hot water dispenser. it ws operated by a manual timer and would simply glow making UV and probably producing ozone

Steinitz did sell a "HPS fixture tester" that apparently works like this
http://web.archive.org/web/20020610173901/http://www.steinitz.com/4HighBayindustrial.html#ST-723a

I think there is rather standard glow lamp with some spark gap in series. The single wire one respond more to dV/dt, so it won't spot the lower igniotion pulses with sharper edges (interturn's short)