From a signature by RonanWaide:

‘F’ is group reply. This is because ‘G’ is for sort and ‘g’ is for get new mail. And ‘G’ is for sort because ‘sort’ used be called ‘group’, and anyway ‘S’ is for save mailbox and ‘s’ is for file message in folder, because ‘f’ is group reply and ‘F’ is group reply including original text.

this is really funny - LathI

Other mnemonics are a Gnus fortune file available here (note: the link is defunct as of 2010-04-21):

Add the gnu_tips.dat and gnus_tips file to a ~/fortune directory. You can add your own gnus tips to the gnus_tips file (don’t forget the % separators!), and create a new gnus_tips.dat file for fortune using the strfile -r gnus_tips command.

You can then email gnus newbies from a group to which you have set the posting style thus (’G p’ to edit the group parameters):

   (concat "kester\n--**--\n\n"
	   (shell-command-to-string "fortune ~/fortune")))))

This puts a little gnus ‘tip’ for your newbie friend as a signature…