The Tank Scope is a sight attachment in Unturned 3. It cannot be obtained normally, and is used on the Tank Cannon, and HMG. Unlike other sights, it doesn't have any iron sight model, and to the gunner, using the sight just zooms in on the crosshair slightly.
It appears as #NAME while in the inventory, and equipping it to a gun with a sight already attached will duplicate that sight. With no sight equipped, it will disappear once a sight is put on.