snip.. the cops ...snip...
Cops? over a "conflict"? I marked my tools to find them when I put them down, and with bright colors to spot them easily.
If I find a pink tool on a car Im working on, Im gonna wipe it off an throw it with the rest...
If you are going to steal, why worry about numbers? Just grind them off and be done with it. "Can't prove nothin."
If you find one of my tools under a bench, but it's not engraved, you'd "wipe it off an throw it with the rest"? I'm going to assume there is something missing from your post, related to writing on the internet, and not believe you just admitted to being a thief when it suits you.
In any case, the OP asked for ways that DIDN'T permanently mark the tool. I didn't say that all my tools are engraved too, but they are. Engraving won't help you find it under a table, or on someone's workbench. And it won't keep the pawnshops, flea marketeers, or yard salers from selling them. Nothing will.
I don't really understand the unwillingness to mark your tools though. They are your livelihood. From what I've seen on GJ, mechanics have a SUBSTANTIAL investment in tools. Don't you want to do everything possible to keep them? As far as hurting resale... when will you ever sell them? I look at the "Show us your toolbox" thread, and it doesn't look like anyone on GJ ever sells anything! (Except when buying to resell.) Granted that the members here may be extreme cases, but it looks like most just keep buying more or bigger boxes to hold their ever expanding tool collection
Bright colors, that are uncommon in your shop, whether tape, paint, heat shrink, or something else, are your best bet to quickly get something that 'wandered' back. If you can't see it, you won't get it back. You aren't trying to win a court case, you're trying to keep the occasional borrower honest.
Buying quality, used and cheap, will keep the sting down when stuff does occasionally go missing. Knowing that you are still making payments on tools you don't have, will eat you up.
Good luck,
zuk