Specimen notes are issued to let other banks, and treasuries know about newly issued notes, that are about to be released.  They may released in sets or as individual notes.

Many times theses notes will have all zero serial numbers.  To keep them form being used as actual currency ( they are not legal tender, nor are they redeemable ) they will perforate or over-print the notes with Specimen or similar wording in their country's language.  Some of the wording currently used is as follows:

The quantity and distribution is of specimen notes is normally very limited making them more expensive than the regular issued notes.  Some countries like Bahrain produce greater quantities of specimen notes, and the serial number is preceded by the Maltese cross.