Out of curiosity, what evidence would convince you?

I don't know - isn't this an issue with the erosion of trust towards the administration and "domain experts", something they can only blame themselves for?

More importantly, why do you want people to be convinced of this? What difference does it make? If it is used as some sort of justification for (more?) economic sanctions or an attack, then I don't think any realistic hacking attempt is going to be enough. If you just want this attributed to NK, what is the point? If people don't know enough about the situation to be sure, and they have no trust in any authority on the subject, then the way forward would be for an authority to build up trust with those people and then claim it is attributed to NK.

Absolute certainty that this would not be used as an excuse to launch military attacks would be a start.

Collin Powell got quite a lot of tonnage I mean mileage out of a cartoon drawing. Just draw him a picture.