In ancient China, the Chinese regarded the names of their emperors and elders as taboos. It was forbidden to write the name of an emperor when quoting anything old or composing anything new. To avoid such problems, later emperors were given names with characters invented for them -- characters that were utterly useless for any other purpose. 

To illustrate the principles involved here, let us take up the case of the man who founded the Ming Dynasty (1368-1644). As an individual, he was a man of the Zhu family named Yuanzhang, so according to the usual manner he would be called Zhu Yuanzhang. However, once he ascended the throne, his personal name became taboo; thenceforth, he would be referred to by his dynastic name or Miaohao (temple name) Great Ancestor of the Ming, or Ming Taizu. According to the conventions of English usage, we would refer to him as Emperor Taizu.

Since a Chinese character has different elements, or morphemes, and most Chinese names mean something, there were some ways to avoid tattoo words for ordinary people. For instance, a person can use any word element morpheme of a taboo word as his/her name; replace the taboo word with its synonyms or parasynonyms; use homophones or words with similar pronunciation as substitutes of the taboo word; change the pronunciation of the tattoo word when using it; use characters in similar shapes; add components to the taboo character to create a new one and so on.