7.3.1. Clearly indicate mandatory fields
On each form, mandatory fields should be clearly indicated:
A distinctive sign (statement, symbol, pictogram, etc.) must be provided in the label of each mandatory field.
A statement at the beginning of the form must indicate that the symbol or pictogram stands for a mandatory field.
Note
If all the form fields are mandatory, then the statement “All fields are mandatory” may be sufficient.
You can also indicate at the beginning of a form that all fields are mandatory, except where there is an indication that the field is optional in the field label.
Examples

In this example, mandatory fields are indicated with an asterisk.

In this example, optional field is indicated.