Where are the serial numbers on a Stihl 026 chainsaw. What does the blue and white round sticker on top of air cleaner mean?

looking from the top of the saw, the serial number is on the clutch side on a thin metal strip on the housing where the clutch cover mates ,next to the muffler. you may have to hold the clutch brake back for easier sight. i believe the sticker stands for hearing protection.