To add the [sic] notation to text notifying of an intentional spelling or grammatical usage. The word sic will provide a link to wikipedia's page describing what it means.
The Latin adverb sic ("thus"; in full: sic erat scriptum, "thus was it written") added immediately after a quoted word or phrase (or a longer piece of text), indicates that the quotation has been transcribed exactly as found in the original source, complete with any erroneous spelling or other nonstandard presentation.
The notation's usual purpose is to inform the reader that any errors or apparent errors in the transcribed material do not arise from errors in the course of the transcription, and the errors have been repeated intentionally, i.e., that they are reproduced exactly as set down by the original writer or printer.
It may also be used as a form of ridicule or as a humorous comment, drawing attention to the original writer's spelling mistakes or emphasizing his or her erroneous logic. Sic is generally placed inside square brackets "[ ]", or in parentheses "( )", and traditionally in italics, as is customary when printing a foreign word.