Thank you for the replies. I recently purchased a lovely Irish counter dish, and after careful inspection find no trace of the Hibernia mark. Although not very visible in the photo, the date letter on the piece bears resemblance to the "D" letter for 1723, and on the piece the straight part on the bottom of the letter is visible.
The marks on my dish:

1723 marks I was able to find on the Web:

The harp crowned appears to be from the period. As for the maker, I hazard John Hamilton, but the crown that may or may not have surmounted these initials is no longer discernible on the dish.
Many thanks.