Plexar was here

Finally the answer to the graffiti Plexar was here that appears in several games. Verbatim response from the author, Steve Hales:

The game, Slime, was one of my first arcade style games. The aliens that were attacking you, were called the Plexarians. It was an easter egg that I put into Fort in the form of graffiti, hence "Plexar was here". It appeared in a few other games from some friends of mine. Atari ST mostly.

Fort Apocalypse