The initials "M+S" indicate that the tyre is a "winter" type, suited for mud and snow conditions and meets the requirements of the seasonal regulations regarding the mandatory use of winter tyres or equipment, meaning that it can circulate during the winter (from 15 November until 15 April) without mandatory chains on board.
Normally this initial is displayed together with the symbol (optional).
The purpose of the features of this type of tyre, winter or "thermal" is to offer excellent performance on cold, wet or snowed roads by significantly lowering stopping distances while improving gripping in curves even under severe weather conditions. Given these features, regardless of the standard in force for which a replacement is not "essential" at the end of the season, we recommend keeping these tyres only during the winter season where performance is at its peak and replace them in the summer with hot road conditions, hence preventing fast wear and tear that can jeopardise safety.
As we have already mentioned in the previous paragraph, a lower speed code can be mounted for this type of tyre with respect to those indicated in the vehicle registration document (never under Q) but in this case there should be a label placed so that it can be clearly visible by the driver in the passenger compartment where it can clearly indicate the maximum speed allowed and at the end of the winter season (after 15 April and by 15 May) these tyres must be replaced with tyres with a speed code that conforms to the vehicle registration document.