Seems pretty obvious, depends on the context I guess. They are making it known what belongs to them.
Someone is lifting up one leg and ******* on trees, cars, and whatever he wants others to keep away from.. :D
A surveyor is marking your property boundary
Setting their boundaries.
Saying back off, it's mine. <br />
People do this with other people.
It means that they are staking their claim in something or someone, warning others to back the hell off.
Claiming ownership of something I presume