These may help, or not, and all I have are SkyHawk pics, and these first two I just made links because they are gigantic pics (both over 1200x wide) you can tweak and size to your liking.
For legal stuff nothing beats an EPA sticker.
Here is a 48cc one http://kcsbikes.com/pics/motor2.jpg
Just print it at 2 1/4" x 1 1/2"
For the round one, well, it has no motor size marking on it.
You can use this Skyhawk pic if you want, http://kcsbikes.com/pics/motor1.jpg
Just cut the circle and print it as a 4" circle.
Use good thick paper!
But as far as the 4" circle logo goes, make your own.
I do regardless of actual engine size, and they all pretty much
look like this.
Nothing says 'don't bother looking' than your own sticker that says 48cc, just don't use mine, I can get protective about things like that, but you get the idea ;-}