My odd-ball

Having this for as long as I can remember, source cannot be recalled, must have exchanged it from someone else when I was a kid. The 1931 must be the sheet number printed low. The stamp has full gum, unhinged, same colour as the tea stain on my teeth :) Intelligent (or stupid) guess is welcomed, for the fun of it.

tapiapi has recently won a N.E. Borneo Sultanates "Iron Bullet Money", odder than my odd-ball. Must be an interesting subject, I wonder if sstawao has any information on it, since it's here his 'turf'.

Received a 'missed call' from bury1883, inviting me to join his chopstick hunting trip to Shanghai ???