code: public boolean isSignatureValid() {
          try {
              return ECKey.verify(Sha256Hash.hashTwice(content), signature, params.getAlertSigningKey());
          } catch (SignatureDecodeException e) {
              return false;
          }
      }
docs: Returns true if the digital signature attached to the message verifies. Don't do anything with the alert if it
  doesn't verify, because that would allow arbitrary attackers to spam your users.