I know obviously speeds would be a key factor, but is there any spot on way to tell if a device is USB 2.0 or 3.0 such as a flash drive.
On the hardware side, I have been noticing that the plastic in the plug is generally BLUE for USB3.0 and WHITE for USB 2.0.
I also believe there is a special USB "symbol" that denotes a USB 3.x connector.
USB3 has more pins than USB2.
USB1 and USB2 have four pins, two for power, one pair for data. USB3 has those four in the standard place, and two extra pairs for 'superspeed' communication.
Wikipedia has two pictures of this, though I must admit is is not clear when you look at them. It should be much easier when looking at a physical device. (Note that both USB3 ports are blue in the pictures below, which matches @mdpc answer.)
Added the picture from Scott's link here: