Seat Leon 2012 Owner's Manual page 22

20 Seat belts
After the ignition has been switched on, the warning lamp  on the instru-
1)
ment panel lights up if the driver has not fastened his/her seat belt, and
an acoustic signal is heard if the vehicle is driven at more than 30 km/h.
The warning lamp*  is switched off if the driver seat belt is fastened while
the ignition is switched on.

1)
Depending on the model version