I found a photo of the button I couldn't remember. Back in 2011, Pike1313, a T-Net digger, posted (in the What-Is-It? forum) a group of very unusual buttons he had dug in Utah. They turned out to be mid-European, mostly from the World War One era. Some were military, and some were European Fire Department buttons. One showing a cannon and something else crossed atop three cannonballs was an Austrian Artillery button from World War One. I saved his photo of the group. At the bottom of the photo below, you'll see a button with a large-size number 5, which has a period or dot at the lower right after the number. As I indicated in my previous post, the presence of the dot leads me to believe your 42 button is a World War One Prussian/German or Austrian infantry regiment button. Prisoner-of-War soldiers from those countries were held in remote prison camps here in the US, and probably some in Canada also, where you dug the 42 button.