Steve Hoefer from Grathio Labs has a nice how to on marking your tools. This covers both marking for preventing mixed up tools as well as marking to recover stolen tools. Both of these things seem to be good ideas as more and more of us work together at community workshops and hackerspaces.
I also work at community workshops quite a bit, and while they often have a lot of tools around I sometimes like to bring my own. (Especially drill bits which seem to always be dull and in exactly the wrong size.) It’s best if my tools don’t mix with theirs.
And finally, tools add up to be a pretty big investment, they sometimes like to get themselves stolen. It’s good to mark them in a way that might prevent that or aid in their recovery if they are.