An asterisk (see also splat, ASCII). Oh, you want an etymology? Notionally, from "I regret that I have only one asterisk for my country!", a misquote of the famous remark uttered by Nathan Hale just before he was hanged. Hale was a (failed) spy for the rebels in the American War of Independence.
Link map
Entries that mention this one are on the left, entries it mentions on the right. Every box is a link.