CHANNEL MODE r

Usage: MODE <channel> +|-r
r - Registered
This indicates that a channel is registered. (informational only, users cannot set this mode)
Privilege: server


CHANNEL MODE R

Usage: MODE <channel> +|-R
R - Registered users only
When this mode is set the server will check to make sure that a user that is joining the channel has a registered nickname.
Privilege: channel operator
Examples:
/mode #movies +R
See also: CMODE +J