Hmm well its definitely not a sign problem since its just a prop. Could be a random Procedural Objects glitch. But sometimes I may update old signs with better textures and maybe that is the effect you're seeing? I have recently updated the old blank signs to fit in line with the new ones.

More great signs! :) Question - any idea what I'm doing wrong? Sometimes, after the road signs have all the text, etc. on them and work fine for many days, the font gets really small and I have to redo them.