Copied from FTDNA June 9, 2012

https://www.familytreedna.com/faq/answers.aspx?id=7#1687

The letters at the beginning of customers' kit numbers indicate where they originally purchased their kits.

 

    A - Those who test with African DNA

    B - Those who transfer results through a lab transfer program

    E - Those who test with iGenea, our European associate

    H - Those who tested with DNA Heritage and transferred their results

    M - Those who test with our Middle East associate

    N - Those who test with and transfer from the National Geographic Genographic Project

    U - Those who test at our UK associate

 

See also: National Geographic Genographic Project, 3rd Party Transfers: DNA Heritage, 3rd Party Transfers: Family Finder Results, and 3rd Party Transfers: Y-DNA Results