The letters NG, shown enclosed in a square, which are an acronym for the words No Good.
The origin of NG refers to bloopers shown during or after the credits of a live television show in Japan (known as NGs), but can be used in any field as a form of shorthand for no good.
📅 NG Button was approved as part of Unicode 6.0 in 2010
under the name “Squared NG”
and added to Emoji 1.0 in 2015.