When I browse to random site, I can see in my browser that A's first level contact trusts this site.
Now I can make a decision based on the amount of trust I have on A. Maybe after exploring the site I can mark specific pages or the whole domain as trusted, so people in my network can see the same.
On a larger level I might trust the Country of Finland, who will only mark their official sites as Trusted. This way I instantly know if I'm on an official site or something pretending to be one.
When I browse to random site, I can see in my browser that A's first level contact trusts this site.
Now I can make a decision based on the amount of trust I have on A. Maybe after exploring the site I can mark specific pages or the whole domain as trusted, so people in my network can see the same.
On a larger level I might trust the Country of Finland, who will only mark their official sites as Trusted. This way I instantly know if I'm on an official site or something pretending to be one.