Here's one of the weirdest signs I have seen in Brunei.
Let's now have a look at the wider picture, to see where these signs are placed.
In fact, they are at the top of the short access road to the satellite station behind the Radisson Hotel in BSB. While it is popular with walkers, some of whom do their morning exercise by walking up and down this hill a few times, and others use the road to head into the Tasek forest, there are almost never any cars on it. My estimate is that maybe two or three cars a day use this road.
Sure, it's a steep hill (which is why people looking for a bit of exercise like to use it). But as there are almost no cars on it, there is no opportunity to overtake. Ever.
So why is there a no overtaking sign there? My guess is that there is a regulation somewhere that all steep hills must have these signs, and someone has followed this regulation even though it makes no sense in this case. But who knows?