Sorry to burst the bubble, and thanks for spending your time testing, but the + in the skill description was a typo as pointed out in patch notes. It is a confirmed negative armor debuff to the target enemy. If you check your skill description you will see that it reads "-10" or "-60" if you have it maxed

Again, thanks for spending your time testing things out, I always highly encourage getting the information for ourselves as opposed to relying on what others have said.