In futures contracts, the delivery month is reflected in the symbol name with a letter code. The letters for all 12 months in order are F, G, H, J, K, M, N, Q, U, V, X, Z.
Where do these letters come from? It seems they were picked somewhat arbitrarily.
They are alphabetical, with the omission of certain letters which I assume could be mistaken for numbers, (except perhaps P, and R, like 8?)
They're taken from the back end of the alphabet, ending in Z (ironically like 2), probably to avoid B and D.
Example futures chain: http://www.cmegroup.com/trading/energy/crude-oil/light-sweet-crude_product_calendar_futures.html
Addendum
This theory is slightly contradicted by the option naming convention: http://en.wikipedia.org/wiki/Option_naming_convention
But options may have developed some time after the futures convention was created.
Like most jargon, its compression. Literally they wanted an unambigeous way to display the month and year of expiry in two characters so you could fit more information on a board of limited character set size. Futures traded on exchanges far before electronic systems.
Now we are stuck with the convention and its a pain for electronic systems as they are only unique in limited contexts.
