I ran into a LF photographer years ago who had a piece of string attached to each of his lensboards. He would loop the other end of the string around the focusing knob on the rear standard of his camera. If the string was stretched enough to prevent focusing he knew he was in "bellows compensation territory" so before he unhooked the string he got out his compensation chart (which covered his selection of lenses).

I've thought about using this but started using a checklist instead (it covers even more of my potential screw-ups).