When and how to approach the team?

Where in the Scrum Guide does it say anything about the Scrum Master monitoring the transparency of artifacts? I've looked at all the instances of the terms "Scrum Master" and "transparency" and can't find anything to this effect. One possibility is that everything else is based on a false premise.

Why would the Scrum Master be the one to realize that there is a lack of transparency? I would suspect that someone else - a Developer, the Product Owner, a key stakeholder external to the Scrum Team - would be the first to realize that they do not have the necessary transparency and visibility into the work that the Scrum Team is doing. The person who realizes this may bring it up to the Scrum Master, but they may also bring it up to the team at the Sprint Review or the Sprint Retrospective, depending on who observes it and what their concerns are.

Why would the Scrum Master see something where the team must act, but have no one else see it? Even if the Scrum Master does observe something so concerning, why would they be the one to make the decision that it must be acted upon? Observation is a key aspect of coaching, and a Scrum Master may make the team aware of an observation, but I'm struggling to think of a scenario with the Scrum Master would be in a position to tell the other members of the Scrum Team that they must act on an observation.

The Scrum Master has no power. 



The Scrum Master has influence. 



I'd suggest checking out the liberators:



https://medium.com/the-liberators/the-6-stances-of-a-scrum-master-a0f06…

I did the same thing that @Thomas did.  I do not see anywhere in the Scrum Guide that states the Scrum Master is responsible for the transparency of the artifacts.  I think I see how you could arrive at that assumption when you take into account that the Scrum Master has a responsibility to help the team and the organization to understand and implement Scrum. But I believe that assumption is wrong because the Scrum Master isn't responsible for the artifacts, they are responsible for helping everyone understand how the transparency is important. They also coach the team and organization on how transparency can be achieved but they are not responsible for maintaining that transparency. 

but let's say he finds something in the team where he has to act. not in the retro on a daily basis he 'randomly' discovers something which has to improve.

Does it have to improve or could it just be an opportunity for improvement?  Scrum Master doesn't have any authority to decide.  It is up to the team and organization to decide whether something must improve.  As a Scrum Master you can only suggest something that could make a difference. 

Consider things this way.  Products have stakeholders.  Stakeholders are the ones that drive the requirements. It is then up to the Product Owner to express those requirements in a way that the stakeholders and Scrum Team can understand them.  The Developers decide how to implement and the stakeholders give feedback on the effectiveness of the Developers implementation. 

Now imagine Scrum as a Product and you are the Product Owner. Would you have the authority to tell the Scrum Team and stakeholders that something "has to improve"?  Or could you suggest that a change could be beneficial and let the stakeholders decide if it is wanted/needed?   

In that scenario, you are the Product Owner.  The stakeholders are your entire organization (which includes the Scrum Team).  The team that will be responsible for implementing any changes is also the entire organization. 

How powerful is he to interrupt them and teach them the bigger picture of agile development?

Very powerful, I would hope, but not with a view to interrupting anyone. A good Scrum Master asks powerful questions in order to reveal rather than resolve.

For example:

• Are these artifacts sufficiently transparent?
• What might be hidden, and what might the consequences be?