I think the easiest way to tell the two apart is the display resolution. You can easily see the pixels in an iPad 2 display,while the pixels in the iPad 3 display are too small to see without magnification.
Here is an excellent thread that explains exactly how to tell which iPad you have.
The OP of this thread made no mention of not having the iPads in front of him. This possible scenario was postulated by a Kaykaykay,later poster in this thread.Quote:
Originally Posted by coolstuffs
I think the answers supplied so far in this thread will enable the OP to tell what version he has,whatever his situation.
The serial and model numbers are on the back of every iPad, as well as viewable in Settings.