A symbol in comics drawn next to a character's head to represent laughter, mirth, or happiness. Looks a bit like ╀─╀, but with a curved line. Commonly used in place of actual laughter when a character is in the background, or the scene is otherwise silent.
Do not mistake for the Chinese radical " 艹 ", which is often used as a shorter and more euphemistic form of "cao" (a Chinese swear word that translates to "fuck") when typing/writing.