In India if we are ahead, and road is not straight, means a driver behind me can't see far, I will blink the directional blinker one or twice to tell him that its safe to overtake me now, from this direction.

A headlight flashes to incoming driver is saying, I see you want to overtake, don't, let me pass first.

A honk at sharp turns on going uphill, telling opposite traffic that I am heavy, cant afford to stop & then start, you give me way if required. There, there is a text painted (officially or informally) "Honk" or "Horn Please"