God doesn't have to prove Himself to anyone about His existence. Nothing on this earth would be in existence if it wasn't for God. Everything came to be by the works of the hands of God. We don't need any further proof to be convinced that God truly exists. All the signs are already made available.
Just like in the parable of the rich man and Lazarus; when the rich man ended up in Hades and pleaded with Abraham to be send a messenger to earth to warn his brothers about hell and Abraham replied the rich man that his brothers have the prophets and other servants of God to listen to.
That is how we likewise also have servants of God who testify of the existence of God by His Word and also through signs and wonders. Therefore, nobody has any excuse. Whoever refuses to believe is doing it simply out of ignorance. Believing in God's existence or not does not make Him any less of God or more of God. In fact, believing in Him is for our own good.
The fact still remains that a creature is created by the creator, whether the creature believes it or not. God is the Creator and we are His creations, His masterpiece. We wouldn't have come to be if He hadn't created us and He created us that we may worship Him.