What should I do if I have accepted an ink-stained euro banknote marked by an IBNS?

If you have accepted a conspicuous ink-stained banknote, you should bring it to a credit institution and provide information about the origin of the banknote. Your bank will submit the note to the National Bank of Belgium which will involve the competent authorities (police), where it may serve as evidence for further criminal investigations. If the ink-staining is not from an IBNS, you will receive a new banknote, provided that the banknote is genuine.