As soon as I had a few Raspberry Pis, I began to realize that knowing what the MAC address was for a Pi was handy, so I put a label on each Ethernet connector with the MAC address.
In working on the Midland Hamgate with multiple TNCs, I was having some initial issues that seemed to be related to the particular Raspberry Pi. At that point it became obvious that I needed quick access not only to the MAC address, but to the name my dnsmasq server would assign to that Pi. So, more labels:
|MAC and nodename labels|
|I2C address labels|
So now my TNCs are all covered with stickers, but they seem to like it. As best I can tell, they are all working: