I don't think they are signatures of Thomas and Ellen on the 1852 marriage cert.
They look the same as the two names in the Name and Surname box,
so were probably written by a third party, possibly the officiating
clergyman.
He also described Ellen incorrectly as Ellen Abigail Dorothy, rather than
Doherty, although the "signature" which looks to be identical,
does have Doherty
David