That's Marcel Bresink's Hardware Monitor (or Temp Monitor.) You must have migrated it from another Mac. I think it just means that Marcel Bresink, all of whose programs are well regarded and trusted, has not, can not, or is unwilling on principle, to participate in Apple's code signing nonsense, either for Gatekeeper or for entry in to the App Store. I'm not running ML, but the default Gatekeeper option in Sys Prefs>Security must be set to the highest. You can adjust that setting, so the program will run. Maybe there's even a whitelist so you can allow poor Marcel Bresink to be an exception.
Message was edited by: WZZZ
This issue has nothing to do with codesigning.