I do believe LCRT or how ever that element that plays the role of LCD is called is what you're looking for. Deco it and you can make it very dark, so the average user that doesn't pay much attention will probably not notice it, but still a pretty good-ish idea, but impossible to do right now at least since signs ignore all particles and are only currently affected by newtonian gravity distorsion.

Surround everything but a corner of the save with grav wall, set up gmpm by the sign in the corner to distort it until illegible (a temp of 438.15 K should to it) set it up so that the gpmp is disabled when you want the sign used.

no i don't think that would be added some way it's a nice idea but i think that the links cannot interact with the electronics because that would require a recode of the elements because the signs are in a different layer so the cannot be combined.

instead of using particles toching the sign you could use a "activator" particle and a "deactivator" particle.