A sign is something you see or felt by you ( belonging /of something or someone) that give INFORMATION of that thing. Seen by you > I saw signs of enemy movements . There is no sign of him. Felt by you > I am feeling weak suddenly . Its must be a sign that I am going to be sick soon. A sign that I memorized them early in life > Something that you have done that tell yourself or others that you have acquired all the knowledge

'Sign' here means an indication, evidence or proof. The King James Version is an old version of the Bible, with traditional, old-fashioned wording. This is the version which was found in the writer's church when he/she was a small child. At some point later, the church replaced these with copies of the New International Version, with more modern wording. The writer knows the KJV wording by heart - this is evidence of the fact that he/she memorised the verses at an an early age.

a sign here is something that shows you to memorize the Bible early on.