Pointing to an advertising board is akin to revealing an ad on your undershirt.
From the guardian.co.uk
The soft vinyl vest attachment fits comfortably between your vest and undershirt.
From the techcrunch.com
She didn't push the issue, just made sure he bathed and changed his undershirt.
From the kansas.com
With a snazzy, black-and-grey pattern, the performance undershirt also looks cool.
From the ocregister.com
Drenched in champagne, he strips down to an undershirt and is showered again.
From the sacbee.com
All we know is we've never seen anyone wrestle with an undershirt like that before.
From the huffingtonpost.com
Some pitchers want to wear the same undershirt before taking the mound, for example.
From the freep.com
The door swings open, and a man in an undershirt glares at the stranger at his door.
From the washingtonpost.com
Mr Iti told the curators it kept riding up and he had to wear an undershirt.
From the nzherald.co.nz
More examples
Singlet: a collarless men's undergarment for the upper part of the body
A vest, undershirt, or tank top, is an article of underwear worn underneath a dress shirt intended to protect them from body sweat and odors. It also makes dress shirts less transparent. The term most commonly refers to upper-body wear worn by males. ...
An upper undergarment with no collar, and with short or no sleeves, worn next to the skin under a shirt; a singlet or (British) a vest
If the undershirt is exposed then all the players on the team must wear matching ones. Numbers or other devices may be worn on the sleeve of the undershirt (for example, if it is worn with a sleeveless jersey), except that pitchers may not have such devices on their undershirt sleeves.