Thank you, all, for your input. I agree, too, that edge markings have nothing to do with the specific camera which is why I didn't mention it. After the film was dry, I looked at it closely with a loupe on a lightbox; the edge markings look like you took an inked stamp, placed it carefully and firmly onto the film, and then pushed it a bit. At this point, I'm thinking it's a manufacturing "defect." As soon as it stops raining, I've got another roll from the same batch to shoot. I'll see if it reveals this same anomaly.