Microsoft does actually provide some guidance for this in the context of dialog boxes. They suggest a few different approaches which are similar to those found on the web, and to some extent in Mac OS.
To indicate that users must provide information in a control, consider the following options:
- Don't indicate anything but handle missing required input with error messages. This approach reduces clutter and works well if most input is optional or users aren't likely to skip controls, thus keeping the number of error messages low.
- Indicate required input using an asterisk at the beginning of the label. Explain the asterisk using either:
- A footnote at the bottom of the content area that says * Required input.
- A tooltip on the asterisk that says Required input.
This approach works well if there aren't many required controls, but poorly if most controls are required. If all controls require input, state "All input required" at an appropriate place at the top of the content area. This approach reduces clutter for this specific case.