Well, from reading these posts, how 'bout this....
Use an engraver or letter stamp your initials in a place that is very difficult to get at to grind away - like the inside radius of a power switch or handle- and just paint the power tool cord and strain relief some ugly color or colors. From a distance, you can prove it was yours and back it up w/ yr initials/
BTW - from what I understand, if you engrave or stamp the metal and the theif grinds it off, the cops, if they are so inclined have a method that will bring the engraving or stamping out even if it has been ground away. Something about how the metal is compressed beneath the engraving and stamping.
This didn't do me a LICK of good however, when I found a dust collector that had been ripped off. The cops took the position that "I couldn't prove that I hadn't sold it".... and yes, the thief was a drug informant.
I wonder how all those cross nails ended up in his driveway.
Hope this helps
John Moorhead