Red
The colour helps indicate urgency, but exact behaviour can vary by manufacturer.
Dashboard Warning Light
Seat Belt
Seat belt not fastened. The usual first step is: Fasten seat belt.
Stop safely
Use this as a quick triage label before confirming in your owner manual.
Fasten seat belt
Check the matching manual page for your exact brand, model and year when possible.
What it usually means
Seat belt not fastened.
What to do next
Fasten seat belt. If the vehicle feels unsafe, stop in a safe place and arrange professional inspection.