Thoughts on these disc brake rotors at 530k

[Hammerhead]

Those look like cold flash cracks to me, best I can tell via pic without hands on.
They are caused by the metal being all nice and hot from brake application and then being splashed by cold water (road puddles). Nothing I would worry about.
Brake drums do the same thing, especially common up here in Canada. They don't crack all the way through, and with drums you can tell, where discs you can't. It's not possible to inspect the between inner and outer rotor where the cooling vents are. If you're ever concerned that a drum cracked like this is cracked through, just heat the outside of the drum in the area of the crack with a torch, slow of course, if it's cracked you'll see it plain as day, but it's rare.