If the user doesn't set a specific Icon in (U)Mount Commands settings dialog, a special magic is tried. So a device /dev/fd0 or mountpoint /floppy gets a floppy icon assigned. Also NFS mounts are recognized and a special icon is shown. Every device/mountpoint can be mounted (green button in the buttom right) and if it is only (u)mountable by root, the icon gets a red frame around it. If the user gives his own icon, there are a few important things to keep in mind: all filenames for icons have to look like this: myicon_mount.xpm and myicon_unmount.xpm because only myicon is stored and the rest is appended. The files should be in the mini-icon directory (this is $KDEDIR/share/icons/mini or $HOME/.kde/share/icons/mini).