In addition to the pinyin letters, there are also four tone marks to indicate which of the four tones is to be used. For example, the syllable "ma" may be written "mā", "má", "mǎ" or "mà" | In addition to the pinyin letters, there are also four tone marks to indicate which of the four tones is to be used. For example, the syllable "ma" may be written "mā", "má", "mǎ" or "mà" |