Tamla-Motown
EMI's British Tamla-Motown label had the prefix TMG, presumably standing for Tamla-Motown-Gordy, the first three, in order of creation, of their American labels. The first release, in March 1965, was given the number TMG 501 (The Supremes' Stop! In the Name of Love).
Read more about this topic: Catalog Numbering Systems For Single Records