Don't want to spoil your day, but has their been a test for metals content? May just be my own inclinations, but personally I would start out with the assumption of psuedo-marks on plateware until content is known. In addition, it would help to note the location of where these surfaced. Four letter monograms are not as ubiquitous in the United States as three letter versions and might be related to a commercial user....can't say what is normal for Canada. The "L" at the end might be for "Lines", a common word in ocean vessel trades. Without that metals content to start with, I would keep an open mind on what you have until more is known. Can you photo the entire back side so the experts here might render a judgement on these (and I'm not one of them..just curious). Hope you've stumbled onto something very interesting!