gnus-summary-marking-alist

gnus-summary-marking-alist is a variable defined in `gnus-sum.el'.
Its value is

((read gnus-del-mark "d")
 (unread gnus-unread-mark "u")
 (ticked gnus-ticked-mark "!")
 (dormant gnus-dormant-mark "?")
 (expirable gnus-expirable-mark "e"))

Documentation:
An alist of names/marks/keystrokes.