Sign in Quran

[Cinjin]

what kind of sign or proof would you like/expect to see in holy book like Quran to make you believe in God..

The question is not valid because of your use of the words "sign or proof."

A sign is not proof of anything and is often subject to much interpretation. Additionally, books are used to record proof, they are not actual evidence of their own subject matter.
Your question fails in that it assumes that a book can offer proof of it's own claims.

And for the record: For me, there is nothing that I would even consider that came from the pen of a long dead primitive Arab tent maker that practiced slavery, brutality, and the stoning of one's own wife.