I've been around sawmills since 1970 all over British Columbia and Alberta and I can say I have never seen anything like exactly like that.They do resemble log dogs as I know them but the ones your showing have an extra point at the left end of the top bar. I can see those being used on a log carriage for a head rig to hold the logs in place while the cut is made but I have no idea what the extra point is for. The dogs I,m familiar with would have either another eye at the top to attach a air or hydraulic cylinder to or if they were for a basic bush mill the they would be heavier and thicker on the top bar so you could manually pound them down into the logs with a hammer. A standard 20 foot carriage would have 3 or 4 of these dogs spread out equally to hold the log during the cut. They don't show any signs of hammer blows on the top so I almost think they have another purpose but what that may be I have no idea.
