Earlier quoted context omitted.
I keep wishing someone takes up the frighteningly ambitious idea here: developing a low-friction government approved (through e.g. legal precedent) service for signing data. After a passport/identiy check it would technically just be a highly available service to cryptographically sign blobs, coupled with a mechanism to handle retractions of signed data in case of compromised keys and a decently advanced notification…
There you go: http://www.guardtime.com/
The other comment's DocuSign suggestion comes closer, but I also doubt DocuSign offers support for third parties to do micro-signing through an API.