During the proofreading process there is a standard set of signs and symbols which is used to mark and attract attention to mistakes that need to be corrected in the text. Obviously, both proofreaders and printing and publishing houses need to understand these marks in order to enable a fluid communication. There are several criteria regarding the use of these standard sets of signs and symbols, although they have been unified under a UNE standard (Spain), NP-61 standard (Portugal) or BS-5261:2 (United Kingdom).