[vintermann]

Probably safest to run it in an emulator with no internet access, given where it was found.

[mschuster91]

APKs are signed so assuming OP can verify his own certificate he might be lucky enough to not have to dig that deep.

[diggan]

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.

[mid-kid]

This sort of protection is rather rare for android apps.