According to Cecil-Humphery-Smith, in the book ROYAL BASTARDS, the coats of arms of bastards, which first appeared for the children of King Henry I, are different than for children born within the marriage of the royal personage. Some of these children were given land and titles but it wasn't until the Tudors and Stuarts that they were given titles of nobility and peerage.
"Often, the identity of the putative father can be discovered from the names given by the mother at baptism or registration." Suggested is that if the mother is named Mary Smith and names her child Bill Harrison Smith, then look for a Harrison or Bill Harrison in the records.
Another way that mothers of illegitimate children named them was by the PLACE of BIRTH.
The word Fitz as in FitzJames is an indication that the father himself is recognizing the child but the child will not carry his surname. His or her surname indicates the father's first or last name is James.
*****
I've noticed in my own research in another country in Europe that over a couple hundred years time it seemed very few children were illegitimate in the church records. But when a child was, it seemed they were given a name uncommon or exotic for the common, often repetitive, naming patterns of the others in the church.
There was one woman in the church records I read who had very many illegitimate children. She must have been so poor for her children died early and often. What a terrible life she had and yet she wanted it. I have so wondered about this woman. Was she the one and only town prostitute? Did one man after another take advantage of her? Was she in love with a married man? Was she an orphan? Was she perhaps slow? I see that the priest baptized her children. And I see that when she managed to live past the age of 40 a widowed man married her. Did he just need someone to cook and clean? Or was he the father of all those children?
C 2018-2025 Book Review by Ancestry Worship Genealogy
NOBILITY? So few people on earth have the right to bear a title, but it's fun to learn that you too have some illustrious ancestor. Coat of Arms are fun too - but most people with a surname that has a Coat of Arms have no right to use it: that's just for fun too, to know that SOMEONE with your surname was ennobled. Anyone who gave up their citizenship of another country to become an American citizen also gave up their right to bear arms or carry a title. In those cases where an American got a title through marriage, it's more a courtesy to use it when addressing them here in the States.