Leonardo probably would want you to write in reflection because he must have been left handed. Most right handed people write right to left because you write with your right hand. If you were left handed it would be easier to write left to right.
Da Vinci had writing in a mirror natural to him because he had to have been left handed. Since he was left handed he thought right handed people write right to left so left handed people write left to right.
This picture of the mountain has an x-axis reflection.
This mountain picture has a x-axis reflection.
This is a building that has a x-axis reflection.