For what reason do the following road signs have a different shape than other signs?

1. To enable pedestrians to notice road signs that are posted opposite their direction of walking.
2. Because these two road signs are less important than other signs.
3. Correct answer: To make them more recognisable to drivers, and so that they can also be seen and interpreted correctly even under poor visibility conditions.
4. Because these two road signs are more important than other signs.

WhyStop and Give way signs have a special shape so they are recognized at once, even in poor visibility or from behind. It is not that they matter more than other signs.