These Deuces for the Dead are real $2 bills, burned to constitute a sacrifice and marked for the dead, leaving a ghostly skull at the center of the bill.
The skulls aren't painted or inked they're the result of meticulously burning away layers of the bill to remove the face and so spiritually kill the note, making it appropriate for the dead.
The burned areas have the look and feel of dead patches on the note - they're striking to the eye the touch.
These are intended as offerings and payments to the spirits of the dead and to Death, making choice offerings to working spirits, ancestors, and to Santa Muerte.
They can also be carried as memento mori - reminders of your temporary mortal existence and your inevitable return to the ancestors.
About the Technique
This technique requires burning off layers of the currency with extreme precision. More than a few $2 bills were sacrificed developing this method as a standard and repeatable process.
That said, due to the very unique nature of US currency as a medium (combining paper, metal, plastic, etc.), and differences in how each note has been handled since it left the mint, no two Deuces for the Dead are exactly the same.
These bills are precious currency for the dead, including both ancestors and necromantic associates. They're also choice devotional offerings for all spirits of death and the graveyard.