I believe you are asking about a shirt "placket. The placket refers to the double layers of fabric that hold the buttons and buttonholes of a shirt.
The word placard (noun meaning a sign, a notice, an advertisement) has no direct antonym; the closest would be 'without placard' or 'placard-less'.
Someone has misspelled my name on this placard. A sandwich sign is a two-faced placard!
In French, "placard" is masculine.
the placard have been posted everywhere.
placard means a poster for public display. Example: there was no placard outside.
Le placard (masc.) means the cupboard in English.
The DOT hazard classification system can be used to identify acute hazards.
dans mon placard means 'in my cupboard' in English.
You should place or install a placard along your truck, on the sides, or the front.
It is a DOT hazardous materials placard indicating compressed oxygen.
explosives
The cast of Mon placard - 1998 includes: Barbara Tissier