On crucial core network kit (at small firms), I often print the password and attach it to the device (along with IP address, SSID, etc). Normally the back/underside. Anyone with enough physical access to see it could do a factory reset (or just unplug it) anyway.
I know that I won't be around forever, and I also know that there's unlikely to be a formal, structured, handover when that time comes. I want to make it as easy as possible for my successor because when the shoe has been on the other foot I have appreciated such acts too.