What is correct from this traffic sign onwards?

The traffic sign you provided is a blank round sign with a red border, which indicates a restriction, specifically a prohibition of entry or access.

In German traffic regulations, this sign typically means "No entry." It prohibits all vehicles, including cars, motorized bicycles, and bicycles from entering a restricted area. This type of sign is used to control traffic flow, protect pedestrian zones, or ensure safety in specific areas such as construction sites or public events.

If you encounter this sign, it's essential to adhere to the restriction. Ignoring it could lead to legal penalties, including fines or points on your driving record. Always be aware of accompanying signs that may provide additional context, such as exceptions for certain vehicle types or specific time periods when the prohibition is in effect.