One character, real meaning, and a genuinely cool historical association.

What a Japanese person actually thinks
Strong. This was the character on the Shinsengumi banner, so it reads as disciplined and slightly martial to anyone who knows their history — which is most Japanese people.

Meaning

Literally: sincerity / truth
Actually: Sincerity, integrity, being true to your word.

Scores

Naturalness●●●●●

A common word and a common given name. Zero awkwardness.

Coolness●●●●●

The rare single kanji that works alone. Dense, historical, not overused by foreigners.

Watch out

lowIt's also a very common male first name (Makoto). Some people will read it as a name rather than a virtue — that's not embarrassing, just be ready for the question.

On skin

誠

Orientation: either

Bold brush, if you can get it done well. This is the character that most rewards a confident stroke — and most exposes a timid one.