Slapmark looks far worse than it is, and is done whilst they are alive.
Pigs skin is very thick, and there is a layer of fat beneath. The slapmark only penetrates thse two layers - it is like a tatoo for a human.
Pigs also have what is called transitory pain, that is they resond to a pain stimulus, but then revert quickly to normal.
We find that if you slap pigs whilst they are eating, they jump, and almost immedaietly return to their food and carry on as normal.
The alternative is an eartag, which involves holding the pigs ear, and punching small hole in the ear with the tag.
Again the response is the same, but it can be more tricky to get right if you are inexperienced.
You will need to do one or the other is taking pigs off for meat.