A player settable lock to prevent items from being sold to vendors.
The reason being that I have sold my RR+ for the umpteenth time. It looks just like any of a number of loot items (blue mushroom) and every once in awhile I'll click it by accident. This made me think of my cell phone, which lets you "lock" photos so you can't delete them until you "unlock" them.
My guess is that you'd need to change something in the client - AKA it can't be done, but I thought I'd ask....