The triangle type device was the original trade mark used by William Hutton on Old Sheffield Plated items.
See:
http://www.925-1000.com/silverplate__OSP5.htmlThe trade mark 'Angle Plate' I believe, came into use much later and was used only on Hutton's holloware items. As for the marks, 'W' and 'H' for William Hutton, the William Hutton trade mark, the next two, the 'A' and the sideways 'P' are just guesswork by me, the 'A' may be a quality indicator for the plating, it was fairly standard in the plating industry to indicate quality by such lettering 'A1', 'A', 'B', etc. but there was no regulation regarding these systems, so they are pretty meaningless. The 'P' may just be an indicator of 'Plated'. To my knowledge, Huttons never used a dating system.
I should also say that I made an error in my original reply, I stated that the maker was William Hutton & Sons, this is incorrect, they were only styled William Hutton and Son after 1864, and William Hutton & Sons after 1870. As Lewis Samuel was working somewhat earlier, then the maker was just William Hutton.
One other thing to mention is that William Hutton at this time did not plate the items themselves, they would have made the blanks and then out sourced someone else to actually process the electro plating, this, I assume, was perhaps because they were not in possession of a license from Elkingtons.
Trev.