I've added a few sample pictures to the last two Sigma 120-300mm OS Lens Reviews. Remember, the "Sports" version of the Sigma 120-300 OS is the newer lens and is capable of matching or exceeding the samples shown for the older "DG" lens, so check out both sets.
Sigma 120-300mm f/2.8 EX DG OS HSM Lens
Sigma 120-300mm f/2.8 DG OS HSM "Sports" Lens