God used dirt from the earth to create man. He could have just said the word and man could have appeared. God used water to destroy all of man. He could have just said "poof you're all gone", but He chose to use nature to do His work. He could smote the Egyptians as they chased the Hebrews into the desert, but He chose to, once again, use what the earth had available. Why is it so hard to believe God could have used planets aligning to send his sign?
God is personal. God is transcendent.
Too many people can go into a cave and get commentary out of rock formations and say, "This rock formation looks like Mickey Mouse." I've been to caves where people say that and it is boring after a while because it is all subjective to people's imaginations and interpretations.
God used two witnesses. I've been looking for the verse in the minor prophets but can't find it because I only learned it once. God can hold you accountable because He sent two witnesses. How many people do you have in the Bible giving you a witness? You have sixty six books and maybe you don't believe one of them is accurate or maybe you believe that error crept in. God can hold you accountable because of two witnesses. I already have God's word so I don't need the Catholic church to declare God because Jesus already did.
You can also go by signs and I will qualify that. Satan is the little god of this world and because Adam gave away his federal headship to him, the kingdoms of the world belong to Satan and the power is given to Satan to deceive:
King James Bible
Even him, whose coming is after the working of Satan with all power and signs and lying wonders,
http://biblehub.com/2_thessalonians/2-9.htm
I've read those books "The Gospel in the Stars" and so forth and stopped reading them because they are novel and because the Christian Research Institute gave people a good case not to believe in them.
Because people don't want to believe the truth, Satan will have the power of lying signs and wonders and give them to the anti-Christ. He will basically be able to do some of the stuff that God can do for a time.