Signing data online (chain of trust)

I’m looking for an online service, where you can create an account, and then sign data of different kinds found on other websites. Let me mention a couple of use cases:

Fighting fake news
By signing news articles on a website, you let others know that you confirm what is written in the news article is true (e.g. it could represent something like “I was there, and this text accurately describe my understanding of what happened”).

Verifying research papers
By signing a research paper, you let other people know that you have read the paper and haven’t found any flaws in the reasoning made by the authors.

Verifying open source code
By signing an open source project on GitHub, you let other people know that you have read through the source code and haven’t found any security issues, so it should be (as far as you know) safe to use that code.

This way, data on the web can be a little more trusted. Of course, to avoid bad data to get high trust by creating a lot of fake users and have them signing the bad data, a chain of trust should be used, e.g “I trust Alice, and therefore I trust everything Alice has signed, and Alice in turn trusts David, so I also trust everything David has signed”, and so on (possibly with a maximum depth of 2, or something (could be configurable)).

This sounds quite useful to me. Do you know if there exists such service?

Have you tried Googling for “online signing service”?