I've found instances where people sign their own name on a Marriage Cert, and then make their 'mark', i.e 'X' on their child's Birth Cert. Why would that be, I wonder? I find it puzzling...
Romilly.
There are a number of reasons why literate people use their mark.
Some such as those employed in piece work will use a mark everyday to distinguish their work, it becomes second nature to sign other things with a mark.
Others will use a mark due to the situation they are in. It may be they are in a situation where to show they were literate was to "act above their station in life", in other words signing could bring trouble to their door.
Sometimes a woman would make a mark if her husband was not literate in order not to embarrass him, and vice versa.
In other instances and I have seen this myself in the 1960s if the person in authority tells them to make their mark the people concerned will make a mark.
I witness that at a school in Scotland in the 1960s, all present had full literacy skills many could also read and write French, German and Latin as well as English, yet when told to make their mark on an official form many (roughly one third) made a mark rather than signing their name.
Cheers
Guy
PS some could even spell! (corrected now)