Final answer:
A yellow-pennant shaped sign on the left side of the road signifies a no passing zone ahead, alerting drivers not to overtake other vehicles in that area for safety reasons.
Step-by-step explanation:
A yellow-pennant shaped sign on the left side of the roadway indicates a no passing zone ahead. This sign is a warning to drivers that they are approaching an area where overtaking and passing other vehicles is prohibited for safety reasons. This type of road signage is vital for pedestrian safety and helps to prevent accidents where visibility is limited or passing is otherwise dangerous.