Final answer:
A vehicle driver preparing to turn left in front of an oncoming motorcyclist signaling for a left turn should wait for the motorcycle to pass and ensure that it is clear to complete the turn. This is crucial for the motorcyclist's safety.
Step-by-step explanation:
When a motorcyclist is signaling for a left turn, a vehicle driver preparing to turn left in front of the motorcycle should wait for the motorcycle to safely pass and ensure that it is clear to complete the turn. This is important for the motorcyclist's safety because motorcycles are smaller and more vulnerable compared to other vehicles on the road. By waiting for the motorcycle to pass, the driver can avoid any potential collision and ensure the safety of the motorcyclist.