A busy mini-mart near me had what musta been a misunderstanding, which lead to the cashier checking and using the pen on every bill used there. I stood in line waiting to pay for my coffee, and the two ones I handed over were checked closely.
The next time I stopped there, they were back to their normal procedure.
If the were metal foil strips, just cutting the strip into short segments with a razor blade would probably be sufficient. A number of short cuts across the strip shouldn’t be very noticeable.