index (n.): a character used to direct particular attention (as to a note or paragraph) and as the seventh in series of the reference marks — also called fist or hand

The index or fist was remarkably enough considered a piece of punctuation, standard in typesetting, for a certain period of time — I’ll go out on a limb and hypothesize that it’s between about 1840 and the end of the First World War. This is why, I suppose, it appears on old timey posters and ersatz old timey posters (see under the word “NOTICE!”), and serves as a recognizable denoter of that vague, undefined cultural era. What I find especially delightful, though, is that through the wonder of Unicode, this character has survived to this day (at 261E) and thus can be copied and pasted directly into my post, like so:
☞