Well this question isn’t just my question, there are many looking for an answer. Skeptics, Agnostics and Atheists all of them have the same question. Most of these people are non-believers. The most common reason for Disbelief (as explained by them) is – “We are very scientific. We do not believe in something that cannot be proven!”
But that’s kind of contradictory and stupid, right? Why?? Simply because – When proof is possible, faith is impossible! If you know all of the answers, you don’t need any faith. If you have absolute conclusive proof of any thing, it requires no trust to move forward.
The answer is simple: If He proved himself to you (and it would be easy for Him to prove Himself, he often has) you could never be a believer – you can never be an Aasthik – you would simply be a FOLLOWER! Would you?
By not coming forward – God has given you free will. Free will to make your own choices, to make your own decisions, the choice to be a Theist or an Atheist, the choice to decide your own fate, future and destiny, the choice to pray and worship the way you want, the choice to contribute to his creation the way you choose to.
To understand it better, you can compare it with democracy - you have freedom. If He decides to announce himself publicly, you would have no choice but to follow him… Which is better Democracy or Dictatorship?
But he has indeed left signs of his presence, the ‘Fibonacci Spiral’ is said to be his artistic signature. The presence of life, the position of earth in the solar system to sustain life…etc etc are just some of his marks of presence. Many great saints have experienced his presence, many have even seen him. I bet you at some point of time have FELT his presence too.