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?
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.
Those mandotary fields are marked and explained with post scripts. But in days, it turns unnecessary to explain (as it is unnecessary to print "enter" or "return" on the keyboard key.)
Why is it asterisk?
IMHO, on the other hand, there should be a "sign" that has to occupy as small space as possible by the text fields. And asterisk is the right sign that gets attention but has no meaning. The last but the most important point is that there is a key directly signed to asterisk on the keyboards.
What is next?
I think, watermarked text fields will completely take the place of asterisk and the warnings will appear as border colored text fields :)
Hope it helps.
Historically asterisks are used to indicate an omission. I believe this stems from early typesetting but is still used today especially when swearing in written media.
From this came the idea of omitting sections and having footnotes instead, - and the asterisk was used to denote a footnote reference.
Extend that to webforms - and the asterisk is simply the footnote indicator again. As usual, it gets copied and accepted everywhere...