APKs are signed so assuming OP can verify his own certificate he might be lucky enough to not have to dig that deep.
If it's being distributed by a piracy site, and the game had any sort of protection to make sure people actually bought it, then probably they're storing/offering a pre-cracked version, which certainly shouldn't (or wouldn't) be signed by anyone.
If it's being distributed by a piracy site, and the game had any sort of protection to make sure people actually bought it, then probably they're storing/offering a pre-cracked version, which certainly shouldn't (or wouldn't) be signed by anyone.