I believe the best indicator of high testosterone is libido. This is not something I can directly observe with majority of the men I interact with, but I see it with my close friends and can get a sense of it from men in general. High libido = high dopamine = high test
Black men have naturally higher level of Test, but also higher levels of E, which is why many of them are often quite emotionally volatile. With them, the most obvious symptom is increased muscle mass, which is also genetically determined, but i'd say the secondary sure-fire sign of high T is your ability to gain muscle/strength.
Things like confidence, dominance, etc can actually be highly serotonergic and I'm sure we've all known men who have "zen like" qualities, not overtly masculine, but can take charge and lead people with a calm and rational mindsets, this doesn't require high T.