Grab a $10 polymer note. On the reverse of the banknote, you can find the word ‘Sports’ on the bottom-left corner of the note. However, you may notice a square dot or even two below this word, with a length of exactly 1 millimetre. Sorry, this does not work for paper notes!
Notes with one square dot have been circulating since January 2008. Earlier this month, notes with two square dots entered circulation. If you have not seen them, try withdrawing from selected Automated Teller Machines (ATM). Many collectors remain puzzled about the presence of these dots.
Similarly, if you have $2 polymer notes, there may be a single square dot located below the word ‘Education’ located on the reverse. Every note in a stack of 100 mint banknotes obtained from the bank has the same number of square dots, if any.
According to the Monetary Authority of Singapore (MAS), this is a new security feature which has been introduced recently for the Central Bank to authenticate the note and is not meant for public knowledge. In addition, there may be other shapes, such as circles, stars or triangles.
In my opinion, the serial number may play a part in determining the pattern found on the note. Just like having a suffix after an NRIC number (which can be calculated from the prefix and number) or the last alphabet of a car registration plate (which can be also calculated from the prefix and number), the pattern may be derived from the serial number. However, a larger sample of serial numbers and their corresponding patterns are required to confirm this hypothesis. Each batch of banknotes may have a different pattern.
However, it appears that the prefix alone does not play a part in the pattern. I have two notes with the same prefix but with a different pattern. The note with serial number starting 2GN117 has one dot, while another note with serial number starting 2GN537 has two dots.
These new polymer notes are printed by Orell Füssli Zurich (OFZ), Switzerland.