Alas, a lot of the general population, certainly in these earlier years, were generally illiterate; thus when required to append their signature to these legal documents they would simply scribe an 'X', leaving the registrar to write the name for them.
I volunteer at our local Register Office, collating and checking registers onto a searchable online index. This requires going through each register for the local area and inputting details onto a database. This last week I did a 500-entry register of Births from 1891, for the area of Leamington, Warwickshire - there were surprisingly few 'X' entries and it was interesting to see how well even the possibly lowest educated person at least had the skills of reasonable penmanship!
The week before, I was doing a Marriage register for the same area but from 1837 - far more 'X' entries that time! Mind you, some of the incumbent Ministers of the parish concerned seemed to have almost illegible writing - 'a', 'e' and 'o' took a bit of guesswork in interpretation on my part; likewise the fashion for not crossing the 't' mid-word. It required a bit of detective work to determine whether they meant 't' or 'l'!
Mind you - here's my 2xGreat Grandparent's marriage recorded in the parish register for Wetheral, Cumberland, 1835:
(click on the picture to enlarge)
He managed to make a good signature but she, poor lass, had to make her mark - and couldn't even manage a 'X'!