Steve Hoefer (a fantastic maker who I interviewed on the Make: Talk podcast earlier this week) has come up with a great way to clearly mark his tools so they don't get lost when he brings them to a hackerspace.
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 bing 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.
So, some identifying marks are in order. There are really two different things going on here, immediate identification, to separate your tools from others, and post-theft ID, to identify the tools as your own.