Since 1988 there has been a sign with orange "egg" on waves. The sign 269 of the German traffic sign catalogue specifically signals: Vehicle owners who carry more than 20 litres of a water-polluting load with them are prohibited from continuing their journey.
With these signs, you almost always have to reckon with fines - this is especially true if a hazard or even an accident with property damage or personal injury could follow the disregard of the sign. It can also be really expensive if you disregard the "water protection area" traffic sign 269.