Spikes that have lately been replacing the traditional (and easily avoidable) barbed/razor wire. These spikes are usually mounted at the top of fences to prevent entry via climbing, hence: anti-climb. These products are usually for private residences of very very VERY important places as the spikes can get pricey. One well known company that manufactures these UEer's bane is Insight Security
The spikes themselves come in a variety of forms. There are prickly beds of them such as these.
Then there are the more evil looking (and assumingly more painful) types. These look more like the normal barbed wire but are much much worse.
This company also produces some less lethal toppings such as their Roller Barrier that will only made you slip and fall (causing more damage to pride than hands)
However, one stipulation remains that will most likely save you from parting with your hands. These highly dangerous fence toppings MUST have a sign posted that is HIGHLY visible that states that these defenses are up. Here is one example of the signs: