What for?

I found this sign board which says "NO AIRCRAFT BEYOND THIS POINT" in the airport. In spite of the warning, there fly lots of airplanes beyond this point. What is this sign board for? It is impossible on earth to read this warning from the flying airplane. Do you know the purpose of this sign? Well, it is written for the airplanes which are to park on the apron. Beyond this line, there lies the threshold of the runway and it is of course dangerous to park the airplane. That's it. It's a kind of trick of a photograph.

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[Corrector]

I found this sign board which says "NO AIRCRAFT BEYOND THIS POINT" in the airport. In spite of the warning, lots of airplanes fly beyond this point. What is this sign board for? It is impossible to read this warning from an airplane when flying. Do you know the purpose of this sign? Well, it is written for the airplanes which park on the apron. Beyond this line is the beginning of the runway and it is of course dangerous to park the airplane there. That's it. It's a kind of trick photograph.