How do i make an item protection script?

How do i make an item protection script?

Like seen in those RPG where you try to pick up other people stuff and they display text like
"This item belongs to someone"
I just need an idea of it or someone may show me some simple methods

well, you could set a variable.
For each item, that is.
if an item is picked up, attach the variable to the item (ownedbyplayerX)

then you can use that as a condition, if item being manipulated is equal to ownedbyplayer(x) then ...