Idea: You can watch an object in the room, in your inventory, on your person, or on another person. An item that is watched will be harder to steal unnoticed, depending on the skill of the watcher.
Examples:
> watch Bob's dagger
> watch coins
> watch bag
ETA:
The same could go for 'guard', which I think already allows you to guard an object in the room. Hence, the addition would be to 'guard' an object on your person, in your inventory, or on another person. Example:
> emote settles both hands over ~bag
> guard bag
> emote settles both hands over %bob bra
> guard Bob's bra
Setting aside "is steal really such a problem, considering how targeted anyone with the skill is when they walk into a room", you can already watch someone you think is a thief, or watch a person to try and catch anything that happens to them.
If guard doesn't protect against theft attempts at least as similarly as it does from coded combat, I can see that needing to be adjusted.
I DO, however, like the idea of "nobody is taking this special package I have for Lord Foofypants, so I will watch it and make sure I never let it go", and by using watch on that object, you are now slightly more susceptible to theft from other pockets.