Letter Mark (LETTER MARK) Letter trademark refers to the smallest writing unit of Pinyin characters or phonetic symbols, including Pinyin characters, foreign letters such as English letters, Latin letters, etc. It can consist of abbreviations, prefixes, meaningless combinations of letters, or even single letters. Due to the limited number of letters, the registration of letters has been strictly restricted. Trademarks consisting of less than two letters are generally not considered to be inherently distinctive, or must be combined with special fonts or colors, or evidence of acquired distinctiveness must be provided, otherwise they cannot receive trademark protection.