I have chanced upon a PDF published by MAS which gives a detailed insight into the security features on our current set of portrait notes and would like to share the link with everyone who is interested!
Also, to clear the myth that Singapore old notes are worthless (All Singapore notes are legal tender unless mutilated), it is officially stated in this MAS publication that:
‘Orchid’, ‘Bird’ and ‘Ship’ Series (Past series)
· Full value will be awarded if both sets of serial numbers are intact and
half value if only one set of serial numbers is intact. The serial number
is considered to be intact if at least four out of the seven digits appear
in full. The prefix is to be treated as one digit
Click
here for full PDF, its an interesting read!