User Modes:

Flag	Information	Description
a	IRC Administrator	User is an IRC Administrator.
b	Empty	This mode is not in use.
c	Empty	This mode is not in use.
d	Deaf	Makes it so you cannot receive channel PRIVMSGs.
e	Empty	This mode is not in use.
f	Empty	This mode is not in use.
g	Empty	This mode is not in use.
h	IRC Help Operator	User is available for Help.
i	Invisible	Not shown in /WHO searches.
j	Empty	This mode is not in use.
k	Empty	This mode is not in use.
l	Empty	This mode is not in use.
m	MIRCd User	User is a True $Network User.
n	Empty	This mode is not in use.
o	IRC Operator	User is an IRC Operator.
p	Empty	This mode is not in use.
q	User is Protected	User cannot be deop/kick/kill by any user.
r	Registerd	Registerd and logged in.
s	Server notice	Can read server notices.
t	Hidden hostname	Is using hidden /vhost.
u	Empty	This mode is not in use.
v	Empty	This mode is not in use.
w	Wallops	Can listen to Wallops messages.
x	Hidden hostname	Give user a hidden hostname (security).
y	Empty	This mode is not in use.
z	SSL user	User is using a Secure Connection.
A	Local IRC Administrator	User is a Local IRC Administrator.
B	Bot	User is a Bot Client.
C	No colour	Strip colour away from private messages.
D	Private deaf	User don't accept any private messages.
E	Empty	This mode is not in use.
F	Empty	This mode is not in use.
G	Swear protection	Strip bad words away from private messages.
H	Empty	This mode is not in use.
I	Empty	This mode is not in use.
J	Empty	This mode is not in use.
K	Empty	This mode is not in use.
L	Empty	This mode is not in use.
M	Empty	This mode is not in use.
N	Empty	This mode is not in use.
O	Local IRC Operator	User is a Local IRC Operator.
P	Empty	This mode is not in use.
Q	Empty	This mode is not in use.
R	Registerd private only	Only receive messages from users with usermode +r.
S	Service	User is a Service Client (protected).
T	No CTCP	Prevents you from receiving CTCPs.
U	Empty	This mode is not in use.
V	Empty	This mode is not in use.
W	Empty	This mode is not in use.
X	Empty	This mode is not in use.
Y	Empty	This mode is not in use.
Z	Empty	This mode is not in use.

You can always use the command /HELPOPS UMODES    for more help.