The StVO § 36 prescribes:
"(...) (1) The signs and instructions of the police officers are to be obeyed, they follow all other orders and other rules, but do not exempt the road user from his due diligence.
(5) Police officers may encourage road users to carry out traffic checks, including checks on their ability to drive and to carry out traffic surveys. The officer may also give the sign to stop by appropriate technical equipment on the emergency vehicle, a Winkenkelle or a red light. These characters can also be used to stop a driver driving ahead. Road users must follow the instructions of police officers (...). "