Identify Motion Sensors

Do you mean you didn't save their serial numbers?

For SS3, slide the sensor off of it's bracket, there should be a small white sticker on the back of the sensor with the serial number.  

If you have interactive monitoring, you can also see the serial numbers of sensors and components by hovering your mouse over their names in the "Devices" list.  You should write them down (and their name/type) and keep them handy (but hidden) in the home, you never know when you might need them.