Hi Jbartlet, first, I'm sorry I won't be of much assistance (mainly because I don't know hardly anything about oil paintings), but I would agree with the posts concerning the masonic symbol. That's what I guessed at first as well. I do, however, know how you feel about giving up
And I also understand the annoyance of wondering what happened to the other paintings (My grandparents had hundreds of marble, Sotheby's quality French furniture pieces that were just taken from the house when they died by who knows whom).
Anyway, back to the important stuff
I would guess that the paintings were done by the same artist, and I would think that they are indeed American, especially since there were so many. That's about the extent of my knowledge on this subject, but I wish you luck! And like others mentioned, just keep looking for the signature. When the internet fails, there are tons of good books out there. Try searching
www.abebooks.com for books on American paintings and artists if you are getting more interested in your unusual painting. Sure is beautiful! And most of all, concerning value, I think the 2k restoration was worth it. I honestly do. It has preserved the piece is great condition I assume and it is a family treasure surely to be enjoyed for a long time, even if it has no monetary value.