1) The Spirit of God indwells a person BEFORE they believe, else they would not call upon the Lord Jesus Christ.
Joh 6:44 No man can come to me, except the Father which hath sent me draw him: and I will raise him up at the last day.
Joh 6:45 It is written in the prophets, And they shall be all taught of God. Every man therefore that hath heard, and hath learned of the Father, cometh unto me.
Joh 6:46 Not that any man hath seen the Father, save he which is of God, he hath seen the Father.
Joh 6:47 Verily, verily, I say unto you, He that believeth on me hath everlasting life.
2) Evidence of the Spirit of God in a person's life, you ask?
Gal 5:22 But the fruit of the Spirit is love, joy, peace, longsuffering, gentleness, goodness, faith.
Do you have the evidence, bishop?