Calluses.
Real spacemen will be adapted to the sitting in chairs under the overloads lasting for hours, so they will develop a baboon-like sitting part.
Actually, instead of obsolete "sea wolf" (what is the "wolf"? who remembers those extinct underdogs?), a true spaceship captain will be called "space baboon" for his long arms and habit of jumping from branch to branch deck to deck in zero/low-g, and for his big red sitting insignia clearly distinguishing him from weedy rookies.
Also for friendly temper and soft skills.