I have two examples of the number 40 backsaw in my collection. Both are early models with split nuts and recessed medallions. The saw shown in the top two pictures has an earlier looking "VULCAN" medallion, and the spine is stamped "40 Harvey W Peace Brooklyn New York Spring Steel Warranted".

The second number 40 backsaw, shown in the bottom three pictures, appears to be a bit later than the first saw. It also has split saw nuts. This example has a clear, complete etch as seen in the second photo. This saw does not have anything stamped into its spine, and has the arm-and-hammer logo in the recessed medallion.