Derrick,this section will really interest you.Rubber Export Coupons were issued by these entities; British Malaya (handstamped with placenames for issue in various states) (1922-34). Federated Malay States (1935-42). Johore (1934-42). Kedah (1934-42). Kelantan (1934-42). Penang Island (1941). Singapore & Penang Island (1936). Singapore Island (1938 & 1941). Straits Settlements Mainland (1938 & 1941-42). Trengganu (1938 & 1941-42). B.L. & P. (1941). British North Borneo (1938). Sarawak (1938 & 1940-42). The designs of these strongly resemble banknotes. Aidan.
Even 20 years ago, I never like to collect Rubber Export Coupons. They are relatively cheap in those days. But I did buy a piece of it which look more like a stamp than a coupon. It has an elephant on it. I sold it off in 2004 when I revisit my banknotes hobby.
Derrick,the only rubber export coupon that I can find listed in the 16th edition of the 'Standard Catalogue of Malaysia,Singapore,Brunei Coin & Paper Money' is a 1934 10 Katis one from Johore.It is priced at 250 Ringgit in VF grade. The catalogue came out in 2003 to commemorate 43 years of International Stamp & Coin Sdn. Bhd. of Kuala Lumpur,Malaysia. I have got a 1942 blue 5 Katis one from Sarawak,which I paid NZ$25 for a few years back.It is priced at RM40 in VF grade. Do you know what the purpose of the letters were for? My 5 Katis has the letter 'P' on it. Aidan.
I do not know anything about rubber coupons as I have no interest in them. I will put across your question to a friend of mine. He may answer your question.