On Windows, the installer registers the Slicer application during install. This makes it possible to use start command to launch the most recently installed Slicer. For example, this command on the command-line starts Slicer and loads an image:
Slicer can be associated with the slicer: custom URL protocol in the operating system or web browser. This is done automatically in the Windows installer and can be set up on other operating systems manually. After this when the user clicks on a slicer://... URL in the web browser, Slicer will start and the slicer.app object emits a signal with the URL that modules can process. The DICOM module processes DICOMweb URLs, but any module can specify additional actions.