So I wondered and Googled and was surprised...

Hubble angular resolution = 0.1arcseconds = 2.7e-5deg
Orbit 600km

sin=opposite/hypotenuse
sin(0.1as)*600,000 = 30cm

I guess the Hubble could see a number plate but not read it...

Still, I suppose stars are quite big...

(Any maths errors?)