Wedgwood Longfellow Series Plate. 50's ? Paul Revere's Ride 8.5"

Couple of things I was wondering about this plate if I may ask. The incised Wedgwood mark. Wondering age on this plate possibly? Also what possibly do the letters mean (pic 4) ? It measures 8.5. I have had no luck finding many of these on line. My thoughts are that these were more decorative than for serving. 8.5" seems a little small. I have seen many other varieties at 10 or 11" Thx for all the help here once more