I know it's not easy.... but here you go -
1. Use Icon Composer (under Developer/Applications/Utilities) to make a new icon if you do not have one.
Lets say you make a new icon named 1.icns
2. Fire up terminal and transfer this 1.icns to the target drive/volume. For example "USBFW300"
you will also need to change this icon name to ".VolumeIcon.icns"
In terminal type in:
cp 1.icns /Volumes/USBFW300/.VolumeIcon.icns
. is the hidden file indicator to tell OS this is a hidden file from Finder, that being said you will not be able to change 1.icns
name to .VolumeIcon.icns if you plan to do that from Finder. Must done in Terminal.
If you have the developer tools installed, fire up a terminal window and type:
/Developer/Tools/SetFile -a C "/Volumes/[volume name]/"
For example, for the volume "USBFW300" the command is
/Developer/Tools/SetFile -a C "/Volumes/USBFW300/"
then in terminal, type in
"killall Finder" --> this command is to refresh Finder then the new icon will show up.