User modes

To set a user mode, type: /mode <yournick> +<mode here>

Example: /mode William +d

To remove a mode, simply use – instead of +

Example: /mode William -d

User mode Restrictions
B Marks you as being a bot. This will add a line to /WHOIS so people can easily recognize bots.
d Makes it so you can not receive channel PRIVMSG’s, except for messages prefixed with a set::channel-command-prefix character. Could be used by bots to reduce traffic so they only see !somecmd type of things.
D Makes it so you can not receive private messages (PM’s) from anyone except IRCOps, servers and services.
G Swear filter: filters out all the “bad words” (List maintained by Chat Corner)
i Makes you so called ‘invisible’. A confusing term to mean that you’re just hidden from /WHO and /NAMES if queried by someone outside the channel.
o IRC Operator Set by server
p Hide channels you are in from /WHOIS, for extra privacy.
r Indicates this is a “registered nick” Set by services
R Only receive private messages from users who are “registered users” (authenticated by Services)
S User is a services bot (gives some extra protection) Services-only
s Server notices, see Snomasks Mostly IRCOp-only
T Prevents you from receiving CTCP’s.
t Indicates you are using a /VHOST Set by server upon /VHOST, /OPER, /*HOST, ..
w Can listen to wallops messages (/WALLOPS from IRCOps’)
x Gives you a hidden / cloaked hostname.
Z Allows only users on a secure connection to send you private messages/notices/CTCPs. Conversely, you can’t send any such messages to non-secure users either.
z Indicates you are connected via SSL/TLS Set by server
*This information taken from