When printer escaping is disabled, a character prints as itself; it is sent directly to the output stream. When printer escaping is enabled, then #\ syntax is used.
When the printer types out the name of a character, it uses the same table as the #\ reader macro would use; therefore any character name that is typed out is acceptable as input (in that implementation). If a non-graphic character has a standardized name, that name is preferred over non-standard names for printing in #\ notation. For the graphic standard characters, the character itself is always used for printing in #\ notation---even if the character also has a name.
For details about the #\ reader macro, see Section 220.127.116.11 (Sharpsign Backslash).