affordance - Why does * (asterisk) mean Required on a form field

Watching a video from DIBI conference and Jared Spool mentions the mysterious origins of the asterisk (*) on a required form field.

Where does this come from, why does an asterisk mean required?

Answer

I always assumed it came directly from the asterisk's standard use denoting footnotes in text.

i.e. fields would be marked with an asterisk with a note somewhere explicitly stating the meaning.

Eventually it becomes widespread and users assume it means 'required' without referencing the footnote. Much in the same way we are taught that red labels mean required.