If your iPod has been lost or stolen, the police or the agency you report it to will probably want the serial number of your iPod. The serial number is right there on the back of your iPod. But you probably didn't memorize the number, write it down, or save it in any way, did you? No matter. So long as you still have your Mac that you sync your iPod to, you can still get your serial number. Open a terminal Window by going to Applications => Utilities => Terminal and when the terminal window opens enter the following command:

defaults read com.apple.iPod

and then press Enter. You'll get results that looks something like so:

Results of the terminal command showing the iPod serial number

You'll notice that displayed in these results is the serial number of your iPod. Problem solved.