As a Malaysian banknote collector, we are very familiar with the "Malaysia Banknotes and Coins" guide book edited by K.N. Boon. I am pretty sure on that. But, do we also aware that indeed international collectors have been using a guide book or a catalog for world currency?
Many times, we over heard that the international collectors always quote banknote reference in relation to "Pick Catalog". What is Pick Catalog? Apparently, Pick Catalog is short name that given the collectors in reference to the "Standard Catalog of World Paper Money" in line with the name of founder and author of the book - Albert Pick.
Albert Pick, a German numismatist, introduced the Pick-number system whereby collectors can unambiguously identify and catalogue each banknote based on its origin and variant. By using this system, collectors can always make reference to a particular note without misinterpretation. For instant, P120a is made reference to a country circulating note where the "a" is referred to its variants, be it different in issuance date, signature or printer. He used the prefix code in such that 'P' for circulating note; 'PS' for special issuance; 'PM' for military issuance and etc.
The Standard Catalog of World Paper Money published by Krause Publications in three volumes and currently under the editorship of George S. Cuhaj.