We also use a custom property, called DeviceType. We use that to direct alerts (some alerts look for devicetype = prod server, others switch/router/whatever), and also to filter views and resources. So for example, we can run a report showing low disk space on prod servers by filtering out devicetype = NonProd Server.
It's much, much more flexible and powerful than naming convention (although we still use st/ss/sp in server names, mostly for AD purposes).
For example, say you stand up a new server named spmynewserver. Set devicetype to non-prod, and you can still take it down or reboot it without triggering an alert. When it's ready to go live, just set devicetype = prodserver. You could do the same with any device.