Is the picture a plug going into a socket? Sometimes when you are updating or restoring some iPods over USB you need to plug it into into a power socket using an iPod charger to complete the process. That's why you see that icon displayed. I believe some older iPods required this step so you got with a power adaptor with them.
If that's the symbol you are seeing you'll find it and others at this link:
iPod iconology or what does this picture on my iPod mean?
The text that goes with it is this:
This icon appears on the screen during an update or restore that occurs when iPod is connected to the computer via a low or no-power connector. This can include some USB ports and 4-pin FireWire ports. When this appears, disconnect iPod from the computer and connect it to the power adapter. Then plug the power adapter into a power outlet. The update or restore will complete and iPod will restart to the main menu.
If you don't have a charger you may be able to complete the process if you have a 6 pin firewire cable and can connect it to a powered firewire port on the computer. Another way is if you have an iPod car charger or speaker dock you can connect to. Failing that visit an Apple store if you have one nearby. Your iPod cannot be used until you complete the process.
