Yes, you can park on the sidewalk in Berlin. It’s normal to leave your scooter or motorcycle on the sidewalk here. If the motorcycle doesn’t block the path, and doesn’t sit on private property, you will not have any problems. You don’t need a parking sticker (Anwohnerparkausweis) for your motorcycle, even if your neighbourhood requires it.1
The law says that motorbikes can only park on the sidewalk if explicitly allowed,2 but these rules are not enforced in most German cities. Almost all motorcycles in Berlin are parked on the sidewalk. Tier and Emmy (scooter rental companies) tell their users to park their scooters on the sidewalk.
If you have seasonal plates (Saisonkennzeichen), you can’t park in public spaces during the winter.3 You must put your motorcycle in storage or use a private parking space.