My app was working fine with position updates on a device with 5.1.
Since then, I made two things: Generating a signed apk. Trying to deploy it to a 6.0 device.
Sorry, thats a bug! It's just spurious logging though: Google Play services does some checking to see whether you are a Google app or a regular third party one.
As part of that, it calls the signature verifier and the logging ended up more verbose than intended - it will be fixed in a future version.This shouldn't affect the behavior of your app at all.
From Ian Barber Answer @ here