I've always used HD0-HD1 etc. for harddrives to make it stand out
from the DFx ones, like CDx for CD-ROM's.
But like everyone else says, the pick is yours, u can use just about
anything that makes you feel better

When it comes to DOS and scripts, or DOpus, I often use the logical
disknames, or labels if you prefer like System3: Work: or...
I'm glad that this system, unlike windooze, use the labels equally well!