Here's the full list from object/GSgopherobj.h:

#define A_FILE      '0'      /* Types of objects */
#define A_DIRECTORY '1'
#define A_CSO       '2'
#define A_ERROR     '3'
#define A_MACHEX    '4'
#define A_PCBIN     '5'
#define A_INDEX     '7'
#define A_TELNET    '8'
#define A_UNIXBIN   '9'
#define A_SOUND     's'
#define A_EVENT     'e'
#define A_CALENDAR  'c'
#define A_GIF       'g'
#define A_HTML      'h'
#define A_TN3270    'T'
#define A_MIME      'M'
#define A_IMAGE     'I'
#define A_INFO      'i'
#define A_MOVIE     ';'
#define A_PDF       'P'
#define A_WORLD     'v'
#define A_APP       '!'
#define A_EOI       '.'
.