Apparently it is not normal for the bride, groom & witnesses to sign the copy that goes to the GRO.
See reply 6.
https://www.rootschat.com/forum/index.php?topic=839129.
The copy from the GRO is the least reliable of all, what they hold has been transcribed from the copy held by the local Register Offices
Stan correctly stated in the Rootschat link "What you have is a certified copy. If you want a copy of the original then you have to get it from the local register office." It
was however
usual for the Bride and Groom
to sign the duplicate copy that eventually made its way to the
Local GRO. Reply 6 discusses the certified copies given to a bride & groom on the day of the marriage and to the various formats cetified copies may subsequently be provided in by a Local GRO.
A copy image or cert ordered from GRO Southport today (originally headquartered in London) was a quarterly copy made by the parish Vicars/ Jewish secretaries themselves, rather than one made by the Local Registry Office. The LRO acted as an intermediary for the Registrar General, collating from their area parishes.
From the start of civil marriage registration 1837 the Church of England, Quakers and Jews were permitted to conduct their own marriage ceremonies without the presence of a Registrar, in affect they acted as Registrars as well. Every marriage was registered in duplicate one copy being the parish's and the other duplicate was kept at the church until FULL whereupon it was sent to the Superintendent Registrar (Leeds in this case). The Minister/Secretary was paid a fee of a shilling or two to conduct searches of and to certify any public requests of copies of entries from either of the 2 books he held. At the expiration of every Quarter the Minister/Secretary made a certified copy of all marriages conducted (ie in April, July, Oct & Jan) and sent that to the District Superintendent Registrar. This he checked and forwarded to London along with the duplicate births and deaths for the quarter and marriages conducted under the supervision of Registrars, whether that be in the Registrar's office or other non-conformist church (Baptist, Methodist etc). As such all copies ordered from GRO headquarters are copies and contain no signatures.
As completed books were eventually sent to the Local District Office orders requested from them (if they provide photocopies of the image rather than type or hand written text) will contain the actual signatures and be in every way identical (supposedly) to the other ledger retained by the parish/synagogue.
It was the duty of the Registrar General, London to compile an index to the certified quarterly copies of all the BMD he received from across England and Wales.
It was the duty of the Superientendent Registrar to index all Books held by him in his District Office to enable searches to be made AT his office and the provision of certified copies to the local public (for marriages this implies completed books, was not stated he had to index all the quarterlies before sending to London).
This was all still the proceedure followed by the 1949 Marriage Act (Part IV)
https://www.legislation.gov.uk/ukpga/Geo6/12-13-14/76/part/IV/enacted which is only a few pages long and can be printed as a pdf
https://www.legislation.gov.uk/ukpga/Geo6/12-13-14/76/part/IV/enacted/data.pdfA similar proceedure was enacted and followed in Ireland up to partition 1921 just the GRO was based in Dublin so that was where quarterly copies went (after 1922 split into the separate GRO jurisdictions). We can see the full birth death and marriage pages with the certification footers on the free Irish Government's site for historical records
https://civilrecords.irishgenealogy.ie/churchrecords/civil-search.jsp - such as this certified copy in 1861
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1861/09614/5486707.pdf [attachments relate to 1836 Marriage Registration Act]
Full Clergy Guidance can be read in section 4 here
https://www.churchofengland.org/sites/default/files/2017-10/guidebookclergyfeb15final.pdf as it pertained 2015 prior to the July 2021 marriage changes.