Since SignCut isn't an application developed by Apple so your operating system might block it depending on what your security settings are set to. If this happens then open the application folder and right click on "SignCut" and click "Open".
This works in most cases but if it doesn't then do the following:
1. Click Apple icon, and then select "System Preference".
2. In the System Preferences, click on the icon "Security & Privacy".
3. In the Security & Privacy settings dialogue, you click the pad lock and enter your password.
4. Now, under Allow apps downloaded from, select "Anywhere", and then SignCut will start properly.
