The boot Tina Sanchez used as inspiration for the pattern on Wraith’s back.
For those of you who don't know, Tina Sanchez is a producer at Respawn Entertainment, and also the character designer who designed Wraith. And I just so happened to be lucky enough to meet her in person during an LGBT roundtable conference at GDC last week, and she showed me her boot, which she claimed she used as inspiration for the pattern on Wraith's back.
Here's some photos:
Tina Sanchez pointing at her boot:
Close up on the boot: 
Group photo (only three of these people work at Respawn -- the fourth is me): 
Wraith's back (in-game screenshot for reference):
