These vases were made at Wick, they come in this blue set of colours and in ambery tones. Sometimes they have a sandblasted image on them, as your does, normally something sea-related, sometimes they're plain.
Dennis Mann is an engraver, I doubt he has anything to do with these.
I suspect your "Cog" is actually C 09, a date.
If you dust a little talcum powder over your mark, then run your finger over it to remove the dust from the surface, the marks might be easier to photograph and read.