My shield is the natural place to display my device, Next time I paint it, I need to make the lion bigger.
This shape for a shield is commonly called a "heater." I always wondered what a "heater" was in the middle ages. After some digging, I found this explanation: "Heater" is not a medieval term at all! It's a 19th C British term for a flat iron for pressing clothes. Apparently, an historian was cataloguing old shields, and he called this type a "heater" because the shape reminded him of a flat iron.
At two feet by three feet, it is of a size more suited for foot combat than for jousting.
This is a picture of a 14th Century shield
taken from the Manesse manuscript, which dates to about 1330. The shield extends from shoulder to hip.