What are dye patches?

Question

The dye patches used as a form of security

Answer 1

You mean dye packs? They are packages of dye that explode and coat the money that the thief has stolen and sometimes it sprays on the thief too. The money with the dye on it can't be used because it's obvious its stolen money.

Answer 2

Together with barcode, enhances security to verify a printed document or package.

This allows one to digitally encode uniquely identifiable covert or overt marks. It can be changed periodically making counterfeiting a very short term value or an entirely fruitless task.