The standard “system” to indicate both the number of inks used on a particular job and the side of the paper they’re printed on is a set of numbers separated by a slash. For example, “2/1” indicates that the printed piece will have 2 spot colors of ink on the “front” of the paper, and 1 spot color of ink on the “back” of the paper. And, just to add confusion, these numbers can also indicate blind debossing… so perhaps the better way to think about this system is that it indicates the number of press runs each side of a sheet of paper will be run through on press.