The Buddha is equipped with 32 marks of physical excellence, each of which is adorned with many blessings. A bump on top of the head and a white curl on the forehead that glows are like the fruit of a flower, namely, the merit of practicing the bodhisattva way as a bodhisattva resulted in the 32 marks of physical excellence of the Buddha. One of the 32 marks is that the top of His head is invisible. Śākyamuni Buddha is 16 feet tall, but non-Buddhists with bamboo sticks could not measure His height, nor could they see the top of His head. Neither Bodhisattva Ying-ch’ih (Ōji Bosatsu) nor the King of the Mahābrahman Heaven could see His top. Why couldn’t they? It is because the Buddha won this “invisibility of His top” mark as the reward for respecting His parents, teachers, and lord by bowing with His head touching the ground.

Shijō Kingo-dono Gohenji, Response to Lord Shijō Kingo, Writings of Nichiren Shōnin, Followers I, Volume 6, Page 118-119