The prevailing standard is /Wikipedia:MOS#Article_titles which points us at Wikipedia:Naming conventions (use English) (there doesn't seem to be a specific naming convention that applies), which says "the most commonly used English version of the name of the subject as the title of the article, as you would find it in verifiable reliable sources". So we should, in general, do what other reference works do.  Britannica says "Reichssicherheitshauptamt", FAS says "Reich's Main Security Office", Encarta doesn't seem to have an article at all (even its article on Heydrich is dismal).  A bunch of the holocaust research/info sites, including Wiesenthal, stick with RSHA (link). So it's not immediately clear to me which of these three options (RSHA/Reichssicherheitshauptam/Reich's Main Security Office) enjoys the most common use.   | Talk