Red WarninG (not a virus)

[Tihol Tiholov]

Warner: 1988 90 Q, sitting idle for 2 months.
Got warned yesterday by a red symbol (thermometer with a flag in 
moving coolant) that the car was allegedly overheating.  This after 
about 40 km drive on a coldish -15 C.  Both coolant and oil gauges 
show normal temps.  Under the hood all seemed well: very little 
"hiss" after opening the coolant cap, added coolant just to please 
the gods, even added engine oil.  The symbol came on, even the next 
morning when the car/engine was cold.  It kept dutifully warning me 
over the next 1,000 or so km I drove yesterday.  And this morning, 
after starting in -13 C.  I'm told this has happened before on this 
car, again when it was cold.  So, what sends the signal, maybe the 
dreaded multifuntion switch?  Does it need re-setting to go away, 
cleaning (which) contacts or what?

Thank you all for the incoming suggestions,

Tihol