Stamps, mackerel and soups — they are all prison currency that is the most commonly used in the Bureau of Prisons (BOP). Their exact values vary, but in the end, the idea is based on stamps.
Incoming mail in the BOP has the stamps removed, pretty much eliminating any “new” used stamps. Not too long ago only unused stamps were valid, but then people washed cancelled stamps. Washing is done by erasing the postmarks on the stamps.
Older stamps — singles and new — even cancelled stamps are considered “compound stamps,” which are currently valued at 35 cents each. A book is 20 stamps (or the equivalent of 700 compound stamps). Good mailing stamps that are singles also fall in that group.
The current price may be $11.60 for a new book of stamps from the post office, but our facility is still selling them for $11 apiece. The typical value of a book of stamps in here is $8.75 (or 25 compound stamps) though it can be higher depending on the urgency and quantity needed.
Mackerels have a value of three to four stamps, and soups a stamp or so.
It’s all about the ease of transactions using the commodity involved.