How ‘Abdu’l-Baha signed His name in English: "abdul Baha abbas" – notice lowercase “a” and uppercase “B”

In contrast to many European languages, in Persian, personal pronouns are never capitalized. 'Abdu'l-Bahá followed this established rule and did not capitalize the pronouns that refer to Him. When the book was translated into English, the particular translator employed the convention, common in English, of capitalizing pronouns. It is interesting to note that when 'Abdu'l-Bahá signed His name in English, He used a combination of upper and lower case letters. He, typically, wrote "abdul Baha abbas" — the reference to Bahá'u'lláh being the only word He capitalized.

On the same principle it is the policy of the Universal House of Justice when approving translations of Tablets written by 'Abdu'l-Bahá, generally to have "me" and "my" and "mine" in lower case, following the example given by 'Abdu'l-Bahá in the writing of His own name in Roman letters. Pronouns used in referring to 'Abdu'l-Bahá by someone else, however, are normally capitalized. This policy can be seen in "Selections from the Writings of 'Abdu'l-Bahá" 

(From a Memorandum of the Research department of the Universal House of Justice dated 23 May 1991, attached to a letter dated 20 June, 1991, written on behalf of the Universal House of Justice to an individual believer)