We do not currently know of any antonyms for quotation mark.
The noun quotation mark is defined as:
One of a pair of quotation marks used to denote a quotation in writing. The symbol used at the beginning of the quotation ("opening quotation mark") is usually “ ("open inverted commas") or ‘ ("open inverted comma"), and the symbol at the end ("closing quotation mark") is ” ("close inverted commas") or ’ ("close inverted comma").
