This demonstrates an RDF-only uses of signatures. The idea is to provide a doc to sign, a proof structure, and a private key to produce a signed doc. Below, you can check that signed doc against a supplied public key.
You can follow the process in the comfort of your own browser. Both the sign and verfiy button actions start with a call to a debugger, so you don't have to screw around looking for the source.
PRs, issues and advice welcome. See the main source and the supporting libraries.