Why was Jesus so vague about the signs of his return?

I mean when asked what signs would herald his return, he simply said wars, rumours of wars, famines, earthquakes and signs in the heavens. All those had been happening since man walked the earth,wars, famine, earthquakes, volcanic eruptions,eclipses, comets....seriously there is nothing absolutely unique that could be a definite warning to his return.Was he vague on purpose??