I had a thread a long time ago , searching for this 'Magic' stuff
that was used on adjustemnt trimmers, pots, ect.
Everybody knew what it was, but could not remember what is was..
well I found it at Grainger's and the company website..
I bought a tube of orange for my bench

http://dymon.com/dymon-product.php?product=1142

I have used finger nail polish for decades with no problems.

If I use it on a customers unit, I find a rare, odd color or mix my own special color from several different ones to insure no tampering.

I finally remembered the commercial name for the product: Red Glyptol.

I use a product called Torque Seal. We use it on aircraft parts after assembly to be sure that the part is installed correctly and to check for parts loosening due to vibration. It comes in a tube and is available at Aircraft Spruce for $1.95 a tube. I use it on car radio case screws to assure that no one has tampered with the radio in case of a warranty claim as the stuff will crack if the screws have been loosened. Harry