In French there's quite a few of these small flying characters, "caractères
suscrits" - abbreviations of ordinal numbers (1st, 2nd and 3rd for instance
being 1er, 2e, 3e, "er" and "e" being in the position of your little "o" but
without any line below). That used to be the case not long ago for Mme, Mlle
(madame, mademoiselle), only the capital M being of normal size. That last
use tends to disappear. In ancient handwriting, plenty of words were
abbreviated that way.
This seems to be much more common in French than in English.