These are panel indicators that have an E10 screw-base 240V neon lamp inside them. I saw these featured on a bigclivedotcom video, and love their retro look and the fact that they're neon, so I bought some. You only see these on the UK eBay, but they ship anywhere - $6 shipped to Canada for ten of them.

The lens (which is plastic) and neon lamp easily unscrew. The neon lamp is housed in a plastic lens and has a built-in ballast resistor tuned for 240V use. However, these light up just fine at 120V, albeit at lower intensity.

The clear, red, and yellow units have an ordinary clear orange neon lamp in them. The green and blue units have a green phosphor-coated neon lamp. The blue unit stinks - it just lights up a dimmer green, as you can see. The clear unit isn't anything to write home about either - it uses a different lens design that doesn't refract the light as well, making it hard to see the light from the side. This isn't helped by how low the lamps sit from the lens.

You can of course get incandescent and LED lamps to fit these, of any voltage you desire, which make these really versatile. An incandescent lamp would make the blue unit much more enjoyable.

I will post photos of the neon lamps themselves later.

Ebay link