How should I mark “Mandatory” and “Optional” fields in a form?

Question

I'm making a web app and in the admin panel there is in one place a list of items where (among other things) the administrator can select which items will be mandatory for the users, and which will be optional. I can't come up with a good visual way of representing this. Ideally I'd like a little icon next to the item name, but I cannot imagine icons that would intuitively represent the concepts of "mandatory" and "optional". Any suggestions?

Answer 1

For passive display, an asterisk behind the field label has become the common indicator for required fields. It's fine for an administrative interface, too, though I would keep the notification:

Name *
Age *
Fetish
SSN

*fields are required

For modifying that, A list of fields, with a checkbox column "required" seems straightforward (if a bit dull).

Answer 2

I'd also put the explanation of the indicator before the fields, so instead of

Name *
Age *
Fetish
SSN

* fields are required

I would do...

*fields are required

Name *
Age *
Fetish
SSN

This ensures that when the user encounters the indicator, they already know what it means. It's also good practice for users browsing with assistive technologies such as screen readers (although that may not be a consideration here, it's still worth noting)