Not to get too far off topic but locks are fine to collect as long as you pay attention and know what you are doing. Keys can be harder but still good to collect. Just have to be more careful. Most locks and keys are stamped with the railroad initials by the manufacturer, not the shop. Some are cast but most of those were for the larger lines - but not all. Bohannan made many lock from about 1895-1910 that had a block style lettering cast into the back. (Two distinct font variations) I am wondering if these cast ones really cost that much more or if that was just the standard Bohannan lock for that time period. ...Not sure but the B&MRR had them, as did the MCRR. What is interesting though is that I have also seen a KCRR one and a Georges one as well, (both from Maine) which surely blows the short line theory about cast locks costing too much for short lines.
As for the factory stamped ones, most early railroad locks from New England were stamped on the back raised pad with the railroad initials. (Among early N.E. makers were Jones, Thomson, Wiliam Page, T. Slaight, Sherburn and Wm Bohannon. Some of these may have just been the suppliers names and not the actual makers.) By the mid 1880’s many RR initials were being stamped on the back of the shackle, but some were still on the back pad. It depends on the maker and time period. Getting back to Sherburn Co. Boston, Mass, - early ones were on the back pad and later were on the back of the shackle. To throw a wrinkle into this, the newest and most un-typical Sherburn I have is a B&MRR car lock that has very modern style stamped railroad mark on the back pad. This lock has a “pebble finish” and I have never seen another Sherburn that looks anything like it. It is rite as rain but not particularly attractive as far as old locks go. The good news is that I have never seen an unmarked Sherburn or Wiliam Page so if you find one it is probably legit.
New England RR lock collecting isn’t what it used to be but there are some really cool old ones out there. Prices have come way down though. IMO, most but not all lines had marked locks. The Monson’s switches seem to have been mostly harp style. By looking at the photos, it does not appeare that they even used switch locks at all. That tells me that they didn't have a big vandalism problem there. Perhaps a clue about the need to pay extra to mark lanterns??? I wouldn't hold my breath on finding a marked one.