Earlier quoted context omitted.
I think that's for APs, given pretty much no smartphone has its MAC printed on it.
Oh, true! I thought it was the MAC address in tiny print on iPhones but it's actually the FCC ID and IMEI. On the other hand, all smartphones have the MAC and serial number easily accessible in their settings menu.
iPhones haven't been doing that for years - they have no markings other than the apple logo on the back.