An ungrammatical sentence is usually denoted with an asterisk (*) at the beginning of the sentence. An infelicitous sentence/utterance is usually denoted with a pound sign (#) at the beginning of a sentence in pragmatics. The pound sign has been used in other areas of Linguistics though, such as in phonetics to denote length/type of pause or in computational linguistics to denote an empty space or a white space by the spacebar.
So for example you
you'd see A: What do you do for a living ? B: *I linguistics professor are doing.
A: What do you do for a living ? B: #My daughter likes the colour blue.
