A group of letters or numbers (or combination of letters and numbers), usually placed on order forms or reply cards, to help mailers know the source of each order, and therefore measure the effectiveness of their mailing lists, offers, creative, timing and other variables.
– Allows for measurement of responses; Specific to one segment in a marketing effort and all who receive it; Example: CASAQ12SPIZ42 (Unit, appeal category, fy, package, segment).