Laird,
We are currently doing research on similar marks to which you have described.  They have been found in Royal Navy contexts (HMB DeBraak, HMS Pandora) as well as from several terrestrial military sites, British and American,  dating from the late 18th century to the War of 1812.

We originally thought they may have been related to military mess arrangements.  The pattern of mess arrangement in both the American and British services were very similar during the late 18th and early 19th centuries.  There are, however, some problems with that interpretation.  We are also exploring the possibility they may have been an expression of folk practices. These marks are like similar to ritual marks found in houses in Britain, and possibly some in the United States.  Although military organizations are highly structured and formalized, there are activities that would fall under what we would term a "folk" practice.  We have been working on this for awhile, so I thought I would pass along our current thinking on these interesting marks.

Charles H. Fithian
Archaeologist
Delaware State Museums
> Hello all,
> I have just been shown a collection of ceramics recovered by divers near the
> naval dockyards in Halifax Harbour, Nova Scotia. The ceramics are almost
> exclusively nineteenth century and there are many examples of regimental or
> Royal Navy pieces. However, there are also quite a number of non-military
> vessels that have been deeply inscribed with Roman numerals (usually on the
> foot). There are also a couple of examples of regimental vessels with the
> inscriptions as well, but they do not correspond with the transfer-printed
> regimental number. I was wondering if anyone else has seen similar examples
> from naval/military contexts?
> Thanks.
> Laird Niven
> Dartmouth, Nova Scotia