Tied to a specific character (take it out of hf, right click it on character).
The mark consists of text chosen by the crafter from a list + a hidden function to uniquely identify the crafter.
Can be optionally added to the mouseover of items that character crafts. The character can describe their "hidden function"/mark to others, who then gain the ability to see if items are in fact "genuine" (i.e., you can tell if the mark matches one of the marks you have in your database of descriptions), and also get the ability to describe that mark to others (but not apply it).
I think this would open up a lot of possibilities, not just larping (named swords, signed artwork, etc...) but also
-coins as described in viewtopic.php?f=48&t=45013 (with the addition of a coinpress)
-advertising for crafters as their stuff gets traded further and further afield
-label your stuff so your villagemates know its your personal property (in non-plot villages or within multi-user plots)
The idea is to have a flexible system that leaves it up to the players how to best use it as much as possible.