They are named in honour of Marco Ferris, a pioneer of Yellowstone settlement. Other local features bearing his name include the smaller city of Ferrisville and Yellowstone's moon, called Marco's Eye.
The banknotes of Chasm City - probably Ferris marks but not confirmed by name - are described thusly:
Some money which felt truly unfamiliar to me: strangely textured banknotes with unfamiliar faces on them and surreal, random denominations. I had asked Amelia what they were.
"That's local money, Tanner. From Chasm City." She pointed to a man on one side of each bill. "That's Lorean Sylveste, I think. Or it could be Marco Ferris. It's ancient history, anyway."
"The money must have travelled from Yellowstone to Sky's Edge and then back again-it's at least thirty years old. Is it worth anything at all now?"
"Oh, a little. I'm no expert in these matters, of course, but I think this would be enough to get you to Chasm City. Not much more than that, though."
Ferris marks are explicitly mentioned later, in a single example, and are indicated to be synonymous with the local banknotes:
I offered him half of another wad, cutting deep into the reserves I had taken from Zebra. "Maybe this will ease your troubles, Lorant. That's another ninety or hundred Ferris marks. Anything more, I might begin to suspect you were fleecing me."
- Chasm City (2001)