It should read 1:4-5.6 which indicates the aperture value throughout the zoom range ... f/4 @ 75mm to f/5.6 @ 300mm.
The Mk III has 'Ultrasonic' clearly labelled in gold on the side of the barrel. Not sure about the Mk II but if the lettering is missing, I would think that it lacks the USM.
HTH
According to Canon's website there are two versions of the 75-300 f4-5.6 MKIII, one with a USM AF system the other with a micro motor AF system.
