Back in the day, it was common practice to put a cross on the sole of your boot to keep the devil from following in your footsteps and bring bad luck upon you. Quote from Tom Sawyer by Huck Finn;
I went down to the front garden and clumb over the stile where you go through the high board fence. There was an inch of new snow on the ground, and I seen somebody’s tracks. They had come up from the quarry and stood around the stile a while, and then went on around the garden fence. It was funny they hadn’t come in, after standing around so. I couldn’t make it out. It was very curious, somehow. I was going to follow around, but I stooped down to look at the tracks first. I didn’t notice anything at first, but next I did. There was a cross in the left boot-heel made with big nails, to keep off the devil.