What is the difference between these road markings

(i) There is no difference between the two and both show that you may not pass other vehicles.
(ii) Both shows you that you may not pass other vehicles but yo will find AA6 on all roads and Y3 on a freeway only.
(iii) AA6 shows you that you may not pass other vehicles while Y3 as well shows you that you may not drive over it to turn into the yard or anything else