The sign you’re referring to is known as "Announcement or continuation of the detour, align to the left." In German traffic law, this sign is used to inform drivers about a detour that is in effect due to road works, accidents, or other reasons.

When you see this sign, it indicates that the normal route is not available, and you should follow the marked detour. The instruction to align to the left means that as you approach the detour, the route will lead you to the left. It's important to follow these signs carefully to ensure you are redirected safely and to avoid any potential hazards.

If you have any more questions about this sign or other traffic rules, feel free to ask!