Which traffic sign refers to the actual mass?

Your answer is correct. The first sign, showing "5.5t" with a red border, refers to the actual mass (or total weight) of a vehicle. It indicates that vehicles exceeding this total weight are prohibited from entering or using the road.

In German traffic rules, this sign specifically restricts vehicles based on their actual gross weight, including cargo and passengers. This is important for protecting infrastructure such as bridges or roads that cannot handle heavier loads.

The second sign, with the truck symbol inside a red circle, generally prohibits trucks from entering regardless of their weight. It does not refer to actual mass but to a vehicle type restriction.

So, the key rule is: When a sign shows a weight limit in tons (like 5.5t), it is a restriction based on the actual mass of the vehicle. This helps you differentiate between vehicle-type prohibitions and weight-based prohibitions.