This is an antique stamp hammer, and part of lumber history. A stamp hammer was used to make “end marks” on lumber and logs. These end marks are much like bands in that they are used to identify cattle. Like cattle brands, end marks and bark marks (cut with an ax), were symbols of identification and ownership. As such, the log marks were registered with the state. In fact, “sinkers” or “deadheads” with log marks still belong to the owner of the mark.
While your lumber doesn’t exactly mosey on off down the prairie, lumber was left to float on down the river to a sorting works (or boom, which had many divisions, called pockets), or shipped with other logs to a lumber company via railroad flat car. In either case, unmarked logs meant lost property. Like stray cattle found without a brand, a stray log without an end mark was a finders-keepers prize which could be kept. If unmarked logs were found, the finder could use their own stamp hammer to make it their own property; but when unmarked logs were found while sorting, the company would put the logs into a “bull pen”. The contents of the bull pen were auctioned off to the highest bidder and the boom company or mill would keep the proceeds.
As for identifying stamp hammers, you are looking for hammer with a three to eight pound cast iron head with a design on it. Like branding irons, the marks on stamp hammers are cast backwards so that the embossed design can be read properly when struck into the wood. The wooden handle of a stamp hammer is about three quarters the length of a common ax handle.