Rock on the Bridge Socks
One of the most popular tricks of spycraft is that of the “dead drop” - a place to leave messages for other spies to find. I once read a story of a spy caught on a bridge in Berlin during the Cold War. He was trying to conceal a note in a fake cobblestone, which he kicked into the river to prevent the East Germans from discovering it.
This socks starts out as a plain stockinette, cuff-down standard pattern. Once the sock itself is complete, stitches are picked up around the ankle and worked up in a cobblestone pattern to create a pocket around the leg. A secret pocket, good for stashing secrets. Or, you know, cab fare.