slaughter houses are not required to look for an under the mane brand, only brands that are visible on either shoulder or rump.
on dark horses, you hold the brand on for some number of seconds, and the hair comes back white. On white skin, you hold the brand on longer, and it freeze-burns so that the hair doesn't come back at all and it looks like a hot brand. Having the brand kill the hair completely also makes it more secure because they can't hide the brand with dye.
Ohhhhhh. I didn't know about the under the mane brand.
The hot brand look sounds like the best way to go.