Copied for safekeeping off of the Lead Adventure Forum, as I had it bookmarked but the Great Photobucket Disaster of 2017 left it without pictures. It has now been restored: How to make Neon signs
Following text is all Andy M's
Well....you don't need much. The
making of the sign is just a bit of plastic card and some solder. You'll
need superglue to stick the solder down and a knife to cut it.
Edit: I forgot to mention the other colours that seem to work for me....
Blue Neon: replace GW Mephiston Red with GW Sotek Green.
Neon: drybrush GW Warboss Green to create the 'halo' effect around the
solder letters, then use GW Moot Green to paint the letters. Add more
and more white to the Moot Green to highlight the letters.