Hey Dudrie,
For item's you placed/created in the editor, yes you can. An item is flagged red when it has an owner. If you go to
The Sandbox, you'll see that most items out for display at the shops have the "Owner ID" field filled in.
In GM mode, you will not get a reaction from the owner NPC, however, because the automatic crime system is disabled to give the GM full control. The text will still show red though, with the stealing hand mouse icon, and the item description will include "Stolen" in red as usual.
Sincerely,
Kevin