What are safe hooks?

Display hooks like the first one below should really not be used anywhere, because tripping accidents can happen to anyone, but certainly they shouldn't be used low to the ground, where children can easily trip and fall into them.

UNSAFE! Better Better still

Basically, if the display hook looks like it could be used in a knife fight, it's unsafe. The closed loop hooks are good, as are the hooks with the scanner attachment on the end (so that price and bar code information can be placed there).