Just right of Nam Myoho-renge-kyo on the Gohonzon is the phrase Namu Taho Nyorai. (Gohonzon map here.) 
 

Namu	Namu is devotion (see Nam in Chinese).

And Taho is composed of two Chinese characters, Ta and Pao.  
 

Ta	Ta (to) is a repetition of two radicals — both are images of the visible moon and the unseen moon (the little tail at the bottom is the unseen moon). Ta is a repetition of that which is seen and unseen.   When Taho appears in the Treasure Tower, he joins Shakyamuni and they recite the Lotus Sutra together in the Ceremony in the Air — a repetition of the seen and the unseen (Ta of Taho).
Pao	The Ho of Taho is Pao in Chinese. It is composed of two radicals.   The radical on top is a roof.   And under the roof is a string of rare white jade.

Thus, Taho is commonly translated as "Many Treasures" or "Many Jewels".  

The "many" comes from the repetition in the Ta character. The roof in Ho indicates something that is hidden in a house and therefore not usually seen. It is a hidden treasure. White jade strung together is a belt held by the master of the house or clan. This is a treasure of riches and identity.  
 

Nyo

Rai

Nyorai means "Thus come one" (see Nyorai Juryo).   Namu Taho Nyorai means "Devotion to Many Treasures Thus Come One."

When we repeat (as Taho does) the 16th chapter of the Lotus Sutra, we reveal the treasures of our life. These treasures are both visible and invisible. . .  Like the moon, which is both seen and unseen. Like jade in a house.  

The Treasure Tower is our life itself.  

"In essence, the appearance of the Treasure Tower indicates that the three groups of Shakyamuni's disciples attained enlightenment only when they heard the Lotus Sutra and perceived the Treasure Tower within their own lives. Now Nichiren's disciples are doing the same. In the Latter Day of the Law, there is no Treasure Tower other than the figures of the men and women who embrace the Lotus Sutra. It follows, therefore, that those who chant Nam-myoho-renge-kyo, irrespective of social status, are themselves the Treasure Tower and likewise they themselves are Taho Buddha."  

—Major Writings, Vol. 1, p. 30, "On the Treasure Tower" 

"Therefore, Abutsu-bo is the Treasure Tower itself, and the Treasure Tower is Abutsu-bo himself. No other knowledge is purposeful."(ibid.)

"The true aspect of all phenomena indicates the two Buddhas Shakyamuni and Taho [seated together in the Treasure Tower]. Taho represents all phenomena and Shakyamuni, the true aspect. The two Buddhas also indicate the two principles of the truth as object and the wisdom to grasp it. Taho signifies the truth , as object and Shakyamuni, the wisdom. Although these are two, they are fused into one in the Buddha's enlightenment." 

—Major Writings, Vol. 2, p. 229, "Earthly Desires are Enlightenment"