Final answer:
A double solid yellow line road marking signifies that it is illegal to pass in either direction, and doing so could result in a traffic violation and increased accident risk.
Step-by-step explanation:
The road marking that indicates it is illegal to pass in either direction is a double solid yellow line. These lines are used to signify that traffic in both directions is prohibited from crossing the centre line to overtake or pass other vehicles. Passing in an area with a double solid yellow line could not only result in a traffic violation but also increase the risk of a head-on collision, as the visibility and safety of such a maneuver are often compromised.