Linden Lab Official:How do I keep someone from selling my stuff?

The permissions system can be used to restrict future owners' ability to sell your creations to others. Here are some popular permissions combinations:

No-Copy, No-Transfer

The owner has one copy of the item. Rezzing the object inworld causes it to leave the owner's inventory. The owner can never give the object to someone else (including giving it back to the creator).

Copy, No-Transfer

The owner can make copies of the item. Rezzing the object inworld retains a copy in inventory (great for vehicles or other objects that may fly off or otherwise get lost). The owner can never give the object to someone else, including giving it back to the creator.

No-Copy, Transfer

The owner has one copy of the item. They can sell that one copy to someone else; if they do, they will no longer own the object. This allows the owner to give the object to someone else when they no longer wish to use it. It also allows residents to buy your items for other people (who may be elsewhere or even offline).

Note: Transfer is listed as Resell/Give Away in Edit or Properties.

Warning: Permissions set on an object in your inventory are not applied to contents until rezzed. See "Next-owner permissions FAQ" for more info.