I hope that if you steal from someone they won't just go on with their everyday life. They should have guards on look-out for this item so that if it gets sold to a shopkeep the shopkeep can alert the guards.
Of course, only for valuable items. Perhaps the price limit changes with NPC's. A wealthy noble of high birth might not bother too much about his 500gp ring that was stolen, however, a mid class trader would.
It should also be done in tiers (I'll use Oblivion's Imperial City for example).
Stealing from Mega Rich Nobles (King/Counsilman/whatever): 5-10 Guards in each Imperial City district - 2000gp is the "I'm bothered" part
Stealing from Standard Nobles: 5-10 Guards in the district of the Crime - 1000gp is the "I'm bothered" part
Stealing from High end Merchants: 3-7 Guards in the district of the crime - 700gp is the "I'm bothered" part
Stealing from a middle class merchant: 1-3 Guards in the district of the crime - 500gp is the "I'm bothered" part
Stealing from a middle class civilian: 1 guard in the district of the crime - 250gp is the "I'm bothered" part
Stealing from a low class trader: 50% That a Hired Mercenary from the fighter's Guild will search the district of the crime - 100gp is the "I'm bothered" part
Stealing from a low class civilian: 5-10% chance that a member of the Thieves Guild will search around the district of the crime, and may take a less than lawful approach to your punishment - 50gp is the "I'm bothered" limit
Just suggestions - The actual numbers are subject to change. I would really like this. And it doesn't seem like something too much, other than the scripting. Once found, they could use a standard piece of dialogue. It would be nice for Guards to search me, and Fighter's guild members to threaten me to allow a search, and Thieves Guild to pick my pocket to find out that I have stolen. They would have the item, and I'd need to kill them to get it back. They would trigger a conversation, so I notice it.
It would also be nice to see Merchants hire guards when they've been stolen from various times. Don't hit the same place twice.
Just seems like a nice, more planned out method of stealing, that would require me to spread out, rather than steal from everyone in the Merchant District.