Sorry but I really couldn’t find the tacks/tack holes in the photo. I have honestly never seen that but I have seen lots of strange adaptations by previous users. If the tacks are placed on the ends or on the top of the toe then it might be an attempt to prevent damage from adjusting hammers (much like strike buttons). Another possibility is that they were simply being used as a quick and simple way to indicate ownership, much like some tool owners will paint their tools a specific color or stamp/carve their initials into them. It might also be just hammer practice from a mischievous child. I could see my four year old grandson doing something like this.