We use validator during a transition ("Field Required" | "Validator Field must not be empty during the transition.") and in the transition screen it doesn't show which fields are mandatory with the red star as it does for field resolution.

Example : 

1. In a workflow add a validator "Field required" and select one or more fields.
2. Add a screen during this transition with these fields
3. Publish your workflow
4. Try the transition

Result : No red stars