I would consider returning it to the pawn shop. The iCloud Activation Lock keeping you out is an anti-theft measures to prevent thieves from using stolen iPhones, iPads or iPods. The original owner needs to remove his iCloud account from the device. There are lots of scams online that promise to remove it, but beware. You might be able to get it unlocked at the Apple store if you take along proof of ownership (receipt from the pawn shop), but I’m not sure that Apple will accept that, after all some dirtbag could have stolen it and hocked it at the pawn shop.