What does a black exclamation mark on a yellow background mean on a car?
This sign means "Novice driver". Such a driver is a driver whose experience is less than 2 years.
The triangular sign with the letter "Y" indicates a training vehicle, but not a student at the wheel (although it is often thought otherwise). The training vehicle must be appropriately equipped and used for driving instruction.
The actual answer is contained in the question itself. I will only point out that there is also a white triangular sign with a red border and a beech "U". It means "The Apprentice Driving". Many people think that this sign is equivalent to "Inexperienced Driver", but this is not the case. The sign "Pupil driving" is intended for cars of driving schools, where, in addition to the trainee, there is an instructor. Well, the reaction of other road users to both of these signs should be approximately the same - not to demand too much and be prepared for surprises on their part.
This icon warns other road users that there is a novice driver (inexperienced, kettle, beginner) in this car. For example, we are obliged to wear this badge during the first year after obtaining the rights.
An inexperienced driver is driving. A driver with a driving experience of up to three years.