I will go with the second option of mechanical damage that’s using a chisel to put in many random holes in the steel to make it unreadable for any one.
Yes, this is a very valid idea, and I will definitely go with it since some people cannot easily get access to some non-mechanical equipment to use in destroying the plate. They can easily get access to some harder medals, like hammers, and they can beat the plate heavily and destroy every letter on it.