Best I recollect, the Newports were made by Crescent and Iver Johnson, and I believe yours is one of the latter. If you hop on Google Image and tap in IVER JOHNSON DOUBLE BARREL it'll pull up some photos.
Afraid I can't help you with regard to the three circle marking. If I had to make a wild guess, I'd say it might be a factory service stamping of some sort - perhaps for tightening the barrel/receiver lockup?
I'd only be guessing, and I won't do that. Searched on this and several other Forums using the terms NEWPORT SHOTGUN and IVER JOHNSON DOUBLE BARREL, but came up dry. I'm sure there are folks here who can point you in the right direction regarding price. Just a thought on the chance you intend firing this shotgun; it may have chambers shorter than the standard 2 3/4" we're used to these days, so have it checked by a qualified gunsmith first.
These old " Trade Name " Crescents don't retain a great deal of value. They were sold in hardware stores for the every day man to put food on the table and keep the fox out of the hen house. I have seen them go a gun shows ( in good condition ) for 100 to 150. I saw one go that was in bea-tee-full shape for 200. In the condition that most of these old shot guns survived, in well used condition, I would venture the lower value. As for the circles stamp ( actually it looks like four circles, one is worn away ), many of the odd markings on old American long arms were made by long gone and unknown workers, doing unknown inspections and assembly in a long gone factory. In other words I don't have a clue, it could mean something or nothing. I would guess it means something only to the people on the assembly line at the time.
Thank you RJay, That is what I am here for, the honest truth. This one is on the keep list, I know that this one was my grandpaps. One other question is that there is nothing left on the stock. What should I put on it to protect the wood?