Now I am absolutely certain that I never placed this piece of plastic here. I can remember just about everything that I've ever done on the layout, and I can assure you that this is not my work. So who, then, could be responsible for this?
Just prior to the operating session back in August, two of the more shady members of the crew were back in this area of the layout looking very intently over the bridge in the picture above. They didn't know that I had come around the corner at the opposite end of the aisle and had observed them. Given their reputations, I came back after the session to see what mischief they have may have created. A quick scan of the area showed nothing amiss, so I almost felt guilty about having assumed they were up to no good. Almost. Now it's clear that I was correct. And we know who is responsible for the mysterious campfire.
I'm not one to go around pointing fingers or naming names, but let's just say that one of the miscreants is known to abscond with freight cars at every available opportunity and the other is known to refer to railroad executives traveling on special movements as the "circus train." The good news is that, given their advanced years, I'm sure they have both long forgotten about this little incident.