Why are there stars in the serial number?

Ordinarily, one or two letters followed by six or seven numbers comprise the serial number in Philippine banknotes. Occasionally, we encounter bills with stars in the serial number instead of letters.

If you are holding a bill with a star in the serial number, then what you have is a replacement banknote.

For some reason, an error occurred during the printing of the bills at the Central Bank. These defective notes are destroyed and are reprinted, but this time with a star in the serial number.