Either they are expecting motor vehicle drivers to do what is almost certainly already law, use due care in avoiding collissions. Or, they're making it more difficult to pursue harrassment charges by mandating "give warning by the sounding of a horn and by exercising other precautions as are necessary".
"Your honor, I was simply trying to alert the cyclist to the fact that I was passing and they shouldn't move further into the traffic lane."
__________________
Birth Certificate, Passport, Marriage License Driver's License and Residency Permit all say I'm a Fred. I guess there's no denying it.