Digital signatures allow authentication of content based on a secret held by the signing entity. Are there any existing schemes, proposals or even services for letting "location" or "time" sign the content?
Motivation: Time and space (i.e. geolocation) are fundamental variables in our lifes and their integration in digital signatures could be useful e.g. for impeding fake news or elaborating on new proof-of-** principles for the broader field of "blockchain"-like technologies.
Are there any existing third party services? Or are there even trustless approaches maybe based on distributed computing / p2p-networks / sealed hardware?
Edit 1: I now see there are already some topics dealing with centralized timestamping services (e.g. here). Thus, the emphasis of this topic should be more directed towards trustless approaches.