As ticky-tack as this interpretation historically has been, recently the FAA published their interpretation as to "what is known icing". Here it is for all to heed. When the FED's put it in black and white, you would be best served to comply......

"straight from the FAA legal counsel: "Reduced to basic terms, known icing conditions exist when visible moisture or high relative humidity combines with temperatures near or below freezing. Since clouds are a form of visible moisture, flying through clouds at an altitude that is near or below freezing would constitute flight into known icing conditions. Another factor to consider, as a practical matter, is the temperature of the aircraft exterior. When the air temperature is close to but above freezing, any part of an aircraft exterior that is below freezing may cause water droplets to freeze and ice to accumulate. When the air temperature is below freezing, any part of an aircraft exterior that is above freezing (e.g., engine cowling) may cause snow or ice crystals to melt, refreeze, and further accumulate as ice. The Federal Aviation Regulations do not allow for experimentation. Flight into known
icing conditions when the airplane flight manual or pilot operating handbook prohibits such flight would constitute a violation whether the aircraft accretes ice or not."