Turning the key to MAR the warning light on the dial turns on, but it should go off as soon as the engine is started.
If the 
warning light turns on when
the car is travelling (on certain versions together with the message on the display),
stop the engine immediately and contact a Fiat Dealership.
See also:
7. Turn Signal Indicators
The arrows will flash in unison with the exterior turn signal, when using the
turn signal lever. ...
Heated rear window
The warning light on the dial turns on when the heated rear window is turned
on. ...
If an exterior light burns out
For the type of bulb and power rating, see “When needing to change a bulb”. ...