Android app signature?

[Chip Thomas]

I built the standalone for my app update using the same keystore I used
with the original release.

But when I try to run the APK on my device (emailed to myself), I get this
error:

"Application not installed. Package with that name and different signature
already installed."

After some research, I used keytool to compare the certificate fingerprints
of the META-INF/*APP*.RSA files of both the original apk and the new one,
and they match.  Would that be a good indicator that these should be the
same signature?

I definitely don't want users to have to uninstall and reinstall the app in
order to get this update.

Any help or insight is greatly appreciated!