[Byron]

Yep - used to seeing that on clothing - on sleeve of jacket etc. - but not direct to the body.
In football (soccer) the armband on the jersey indicates the captain of the team.
I am guessing here that this guy with this particular stance is first in a posed line-up (there is another guy close to his left side) and so team captain of something (black would indicate mourning but here I would guess again that there is the coincidence of the team color - there being black in the speedo and swimcap). A sign in the distance might help with location but too vague to read unfortunately.