London bus drivers are required to have a vision with them at all times when they are driving. The nature of this vision, however, is not specified by the bus companies. Presumably then, one driver might maintain a vision of beauty about their person, while another might do likewise with a vision of horror. Yet another might well opt for a religiously inspired vision. Whatever vision the driver chooses, it must be kept active at all times and in full view of the driver while on the road. Passengers are required not to place themselves between these visions and their drivers in order to maintain the safe running of the buses. Furthermore, the passengers must not engage in conversation with any of the visions, regardless of how amicable and forthcoming they may be. The consequences, one assumes, must be dire.
So there we have it; drivers must maintain their chosen vision at all times and passengers must not attempt either to come between the vision and its driver, or to engage in conversation with it. Indeed, this is clearly spelled out on a notice next to the driver's seat:
PLEASE DO NOT SPEAK TO OR OBSCURE THE DRIVER'S VISION
WHILE THE BUS IS MOVING
There is another, highly unlikely, interpretation of this notice: the people who devised it have a rather dubious and tenuous command of sentence structure in English. This hypothesis, though, can be safely discarded as no one in their right mind would go to the trouble of devising such an erroneous notice, printing thousands of them and placing them prominently in every bus in London, where devious-minded English language teachers can see them and dream up improbable explanations for their existence. Perish the thought!