I got close but then I gave up. Maybe you can take my code and get closer.
VIEW:
displayname=Calendar ID
listdelimiter=<br>
listmethod=nested(portalTabSections).lists
textmode=true
type=iterate
valueexpression={calendarPortalSection}.{ID}
valueformat=HTML
This generates a GUID which appears on dashboards that contain calendars and is left blank on dashboards that don't contain calendars. I don't know of a way to get a calendar GUID from the calendar itself but with this view I guess you could cobble together a filter for the GUID you find. Or if not, you can run a full dashboard report, download to excel and just search for all the GUIDs corresponding to that one GUID you are looking for? Good luck!