@SuppressLint("PackageManagerGetSignatures") private static Signature getSystemSignature(final PackageManager pm) {
		try {
			final PackageInfo sys = pm.getPackageInfo("android", PackageManager.GET_SIGNATURES);
			return getFirstSignature(sys);
		} catch (final PackageManager.NameNotFoundException ignored) { return null; }
	}
Determine whether a package is a "system package", in which case certain things
(like disabling notifications or disabling the package altogether) should be disallowed.
shared/src/main/java/com/oasisfeng/island/provisioning/SystemAppsManager.java