Product Signer is an Automator Service for signing packages with Developer ID certificate(s).
Run install.sh and service will be installed in current user's service folder.
In Finder, select one or more packages (or folders with packages), right-click and choose "Services → Product Sign". You will be prompted if you have more than one Developer ID certificates installed. Signed packages will be saved with added _s to their names like so signed copy of MyApp.pkg will be saved as MyApp_s.pkg
Product Signer is available under the WTFPL license. See the LICENSE file for more info.