That leaves us with the possible dates of 18 as year of manufacture. If we check the Bergensen book, we can see that patterns with numbers above 3000 were not introduced until after 1881.
That discounts the possibility that 1861 is the year of production for this piece leaving us with the remaining year 1887.
The Wedgwood company is a British pottery firm, originally founded by Josiah Wedgwood c1795, and possibly the most famous name ever associated with pottery.
Unfortunately it's necessary to note that a monkey wrench can be thrown into this entire process because there were occasions when the first letter and second letter were switched so that the month letter was the second one.
The only way to be absolutely positive that the month is correct is by having either the first or second letter be a letter that was not used during the corresponding year.
These marks can also assist in dating a piece because designs can be dated as well.
(A list of the Wedgwood pattern shapes can be found in the appendix of Victoria Bergensen's wonderful book Majolica: British, Continental and American Wares, 1851-1915.) Let's say the imprinted year date code is a P. There is no ENGLAND impressed on the piece so we can discount 1913 as a possible year of production.