PotMoney?
 

Paper money is made of 75% cotton and 25% linen.
Linen is made from plant fibers of the flax plant and sometimes from hemp.
Hemp is fiber of the cannabis plant.
Dogs are trained to sniff drugs on money or could it be in the money?
Then the money is seized.
Coincidence?

Dogs are trained to smell the drug, not the material.

Industrial hemp production is very difficult to pull off in the US, so I doubt that there is any in any bill printed since marijuana was declared illegal. However, there's always the cocaine contamination to keep you up nights...