message-yank-cited-prefix
message-yank-cited-prefix is a variable defined in `message.el
'.
Its value is ">"Documentation: *Prefix inserted on cited lines of yanked messages. Fix `message-cite-prefix-regexp' if it is set to an abnormal value. See also `message-yank-prefix' and `message-yank-empty-prefix'. You can customize this variable. This variable was introduced, or its default value was changed, in version 22.1 of Emacs.