The latest proposal is:

Prefixes beginning with the three letter sequence s, c, e, or the
four letter sequence s, c, e, _ (underscore), in any case combination, are
reserved for use by this standards group. 

Prefixes beginning with the five-letter sequence s, c, e,
m, i, or the six-letter sequence s, c, e, _ (underscore),
m, i, in any case combination, are reserved for use by SCE-MI
and SCE-MI related specifications.