The signs imply those proofs which testify to the possibility and necessity of the Hereafter. The earth's own body and its structure, its having been placed at a suitable distance from the sun at a particular angle, the arrangement of heat and light and of different seasons on it, the provision of air and water on it, and of countless different kinds of treasures in its belly, covering its surface with a fertile crest and causing to grow in it an endless variety of vegetables, generating countless races of the animals of the land and water and air, providing suitable food and proper conditions for the life of every species, creating and making available all those means and resources on it even before the creation of man, so as to meet and suit his ever increasing needs in every stage of history as well as accord with the development of his civilization and way of living, these and countless other signs can be seen in the earth and its surroundings by every discerning eye.
The case of the one who has closed the doors of his heart to belief and faith is different. He will see in these every thing else but not any sign that may point to the reality. But an un-prejudiced person who has an open mind, will never form the idea after observing these signs that all this has come about as the result of an accidental explosion, that had occurred suddenly in the universe millions of years ago; he will rather be convinced that this wise and perfect work of art is the creation of an Omnipotent and Omniscient God. And that God Who has made this earth cannot be helpless to resurrect man after death, nor can He be so foolish as to leave a sensible and intelligent being like man after granting him powers and authority to roam at will in His earth. The fact that man has been granted powers and authority by itself demands that he should be accountable; otherwise it would be against wisdom and justice.