oh no the Mac Plus might require a load on the +12v line in order for the power supply to stabilize, which is problematic for running it without a computer attached
It's interesting that signatures started disappearing -- mine has far fewer than shown in the folklore page https://www.folklore.org/StoryView.py?project=Macintosh&story=Signing_Party.txt or in the presentation by Kottke.
@jwz and also using xrandr to map the region of the X display that is shown on the external HDMI connector
@jwz this is using the breadboard version of the Pixel Wrangler to appear as an HDMI display to my laptop. https://github.com/osresearch/pixel-wrangler
Booting Linux using the signboard from the side of a train as the display? Easy with the Pixel Wrangler.