Does the SecureBoot infrastructure recognize your DVD *because* it is a msft-digisigned OS, or does the hold-shift-in-win8 procedure temporarily disable SecureBoot, or what?
None of the above. It recognises it because the UEFI firmware presented it as a potentially bootable device. If you attempt to boot off it with Secure Boot enabled, and if it's not appropriately signed, the boot will fail.
Re: SecureBoot setting, versus SecureBoot philosophy
None of the above. It recognises it because the UEFI firmware presented it as a potentially bootable device. If you attempt to boot off it with Secure Boot enabled, and if it's not appropriately signed, the boot will fail.