if it is just round circle with wave inside that is radiator coolant level low
if it is round circle with temp indicator thermometer and wave inside circle that is coolant level/hot indicator warning light.

check your coolant level in resivoir and in radiator (when cold) and see if it is low. If it is low then you may have a leak and need to pressure test system to see where leak is and repair it.
if no leaks found then just top off radiator and resivoir and monitor it... sometimes they just blow out coolant out of resivoir when they get hot... seen many do this for no apparant reason, sometimes it can be radiator cap bad tho... always having to add to resivoir during pm's because of this.