Asterisk is one of those words in English that began as a noun, but is often used as a verb, with the meaning “To mark with an asterisk” (AHD s.v. asterisk). An asterisk is:

n.

1. A star-shaped figure (*) used chiefly to indicate an omission, a reference to a footnote, or an unattested word, sound, or affix.
2. Mathematics A symbol used to indicate multiplication, as in 2 * 3 = 6.

Etymologically speaking, asterisk (present in Middle English) derives from Late Latin asteriscus, from Greek asteriskos, diminutive of astēr, “star.” Asterisk, Aster, and Star are all derived from the Proto Indo-European root *ster-3.

Our practice of using an asterisk to identify things as particularly important, or as a reference to mark that there’s a note or comment about an item has a Classical heritage:

The practice of using a star-shaped sign, an asterisk, began in Ptolemaic Alexandria where the great textual scholar Aristophanes of Byzantium and his student Aristarchus of Samothrace used them to mark repeated lines in the Iliad and Odyssey. Several centuries later the prolific (and self-mutilated) Christian theologian Origen began to employ asterisks in a different way, to signal the omission of certain passages in the Greek translation of the Old Testament. This usage gradually spread as a sign of something missing or hidden, and hence—at the end of a complex trail that winds through classical editions, Bibles, and pornography—when you type your password on the computer, the letters and numbers often show up as a string of asterisks (The Classical Tradition. Edited by Anthony Grafton, Glenn W. Most, and Salvatore Settis. Harvard University Press, 2013. via Stephen Greenblatt and Joseph Leo Koerner “Glories of Classicism.” New York Review of Books. February 21, 2013).