Hi Mark,
Welcome to the Forum.
The maker's mark, or what's left of it, would have been the mark on the left of your image. The dateletter is the letter 't', (the reversed '5'), idicating that date of assay of your ring at Chester was 1944, this is confirmed by the additional mark on the far right of your mark image, this mark is known as the 'Utility' mark and information about it can be found at:
viewtopic.php?f=36&t=14995.
Regards Trev.