They will have different printing indicating that they are validations and giving instructions on their use.
In most systems, the validation coupons are inactive when received from the supplier.
Instituting automated payment systems has required that validations be automated too.
This happens in three ways: The online validator, usually related to bar code technology, is one technique.
A major concern of parking managers is the tracking of validation books, coupons and stamps. A val stamp in the wrong hands (read that cashier) can mean missing funds.