Initialism of Hansestadt Bremen, the German city of Bremen; used on licence plates and informally in other contexts.
Adjektiivi
Initialism of hardblack (describing a pencil that makes lighter marks than a grade B, but darker marks than a grade H pencil).
Substantiivi
(stars) Initialism of horizontal branch.
(slang, seduction community) Initialism of hotbabe, someone pickup artists try to seduce. (Usually followed by a number in the 1-10 scale of physical beauty, e.g. HB10.)