What does a "DK" signature at the start of track 0 sector 3 of a Dragon 32/64 floppy disk?

I’m looking at disk image files for the Dragon 32 / Dragon 64 computers.

The Dragon computers are very similar to the Tandy TRS-80 Color Computer "CoCo" but are not clones and are not the same. In particular the two machines have very different Disk Operating Systems with totally different disk layouts. The Dragons run "DragonDos" while the CoCos run "RSDOS".

Both systems allow booting third-party OSes from the floppy boot sector by executing a command, DOS on the CoCo and BOOT on the Dragon.

Bootable floppy disk sectors begin with the signature OS. On DragonDos, this is LSN (logical sector number) 2, or track 0 sector 3. (On a CoCo RSDOS disk the boot sector and OS signature is on track 34 sector 0).

But I have some disk image files I downloaded (labelled "Dragon DOS 1.0 Boot" and "Dragon DOS 2.F Boot") which instead of an OS signature at LSN 2 have a DK signature in the same place. I cannot find this signature documented anywhere though the DK signature is used for other things in the Dragon ecosystem:

DragonDOS was on a cartridge which puts the DK signature at address C000:

ROM OS:
    Appears in cartridge space $c000-dfff (Cumana system uses $c000-feff)
    Adds IRQ, FIRQ and NMI handling code, uses various Ram hooks

...

$c000:c001  'DK' - used by BASIC Rom init to detect Disk Rom
$c002-c003  Cartridge Init entry point (BRA $c0xx)
$c004-c029  Indirect address table
$c004:c005  Low Level Hardware Command byte routine ($cxxx)
$c006:c007  ($00ea)

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I never used these systems back in the day so they’re unfamilar. I have three emulators but I find them more tricky to use than many emulators. Most emulate both CoCo and Dragon and I’m not sure how much guessing the emulator does when you try to load a file. Usually I can’t get these images to work but sometimes I can’t get any image to work. I’m never sure if I’ve got the right ROM images in the right folders, what needs Dragon 64 and not just Dragon 32. ROMs from one emulator don’t always just work in another emulator that comes without ROMs. MAME is very counterintuitive in its microcomputer emulation setup…

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So the question is, do both OS and DK indicate boot sectors? Is the DK variant documented or not somewhere? Do I have disk versions of the cartridge? – the 00ea is in the same location as above but not everything matches. Do I maybe have something more recent from the retro era that’s based on modified ROMs?