I occasionally nap at airports if I get there for a really early flight and it's delayed or if I'm taking a redeye with an early connection with a longish stopover. If I'm on chairs (and there's a trick to laying across them if they have arm rests) I'll loop the strap of my carry on(s) around my foot. If I'm napping on the floor I'll use one carry on as a pillow and loop the strap of the other around my foot. I don't think doing those matter though, as I've never had any issues at all while napping in airports. Some people even leave notes on themselves to be woken up at a certain time, and generally some stranger will comply.