Was your mother born in USA? Because it was stamped there. Look for the heading 'Adoption Sets the Precedent' in this link
My mother-in-law was born in a workhouse in 1906. I have the workhouse register of births, there is a Remarks column and the only words in the column are legitimate or illegitimate.My mother was born at Twyford House, Acton Lane, Willesden, Middlesex. This was one of London's Work Houses.
I've never seen one like that, but I don't have a contemporary birth certificate for my only illegitimate ancestor who was born after 1837, only a modern copy.I remember seeing my mother's birth certificate in the late 1950s and it had the word ILLEGITIMATE stamped diagonally across it. The certificate was issued in 1910. I have a current one which is normal but I am curious as to when this stopped happening.
I hope you know about Higginbotham's Workhouse website, if not this page is Willesden.My mother was born at Twyford House, Acton Lane, Willesden, Middlesex. This was one of London's Work Houses.
Where have you looked so far - have you tried Discovery?I have been unable to find any records from Twyford House