The traffic sign you mentioned is known as "Exemption from the traffic ban according to § 40 paragraph 1 BImSchG (in conjunction with sign 270-1) - yellow and green badge."

This sign indicates that vehicles displaying a yellow and green badge are exempt from certain traffic restrictions as specified by environmental laws, particularly in areas where there may be limitations on vehicle access due to emissions or pollution control regulations. The badge signifies that the vehicle meets specific emissions standards that allow it to operate in zones where other vehicles might be restricted.

In Germany, this system is often associated with environmental zones (Umweltzonen), where only vehicles that meet certain environmental criteria can enter. The yellow and green badge typically indicates that the vehicle produces lower emissions compared to others that do not qualify.

It's important for drivers to display the appropriate badge on their vehicle to avoid fines and to enjoy access to restricted areas. Always check local regulations to ensure compliance with traffic and environmental rules.