And here they are!
This one would be about 42" or 48" long, for respective heights of 21' and 24".
But this one could fit on a regular 24" x 24" metal sign plate with very legible numbers.
The zuni indicates it's a New Mexico state highway.
(Right now they're kind of green so it looks like I'll have to fix the colors!)
6 October 2014: FIXED! :^D