There are many common questions about road signs and signals, this time we will explain about “headlights question mark”. The sign, which has the code S-24, normally works in conjunction with another, R-413. Let´s look at a common scenario, a tunnel, where there are also some other changes to rules which we discuss another time. We now have to remember one of the basics of traffic signs, circles give us orders (things we must or must not do), whereas squares or rectangles are informative. As we approach a tunnel, we see R-413, a blue circular sign featuring a pictogram of headlights. telling us we must switch our lights on. As we leave the tunnel, we see sign S-24, which is a rectangular sign featuring a pictogram of headlights and a question mark. Now, back to basics again. The approach sign, R-413, tells us we must put our headlights on. But, when we leave the tunnel, a sign cannot tell us we must switch them off, as we could be emerging during the night or in poor visibility, and so S-24, an informative sign, tells us to check if we still need our headlights on or not. As a final note, remember that when we talk about headlights, we don´t mean Daytime Running Lights (DRL), they are not sufficient when it comes to illuminating areas such as tunnels, or at night.