Theft of a tailgate is probably more of a grab and run thing, so if they are slowed down even a little it might prevent it.
That said, I have never had anything to lock mine on ...
Just last week, tho, I was at my favorite u pull, and my buddy was eyeballing a gate on a '94, straight and solid, bad paint, cables both broken, and when we went to lift it off there was a clamp, sort of like the bands that the factory used to hold tail pipes to the rear hanger, just a band with a self tapping bolt clamping it together.
It was painted body color, and appeared like some sort of factory applied deal. Never saw one before.
Something made me think it may have been a mexican market import truck, maybe it is done out there.
So, we went a few rows away and found a nice paint,no rust, no dents, good cables one on a '01, same price.
$45