User modes allow for a variety of functions. Most user modes are usable only by IRC Operators, but there are some modes that any user can set. 

The command for setting a mode is /mode nickname +?, where nickname is your own nickname (Note: Users cannot set modes on other users), and ? is the letter code for the mode you wish to set. You can remove a mode using the same command, replacing the + with a -. You can check the modes you have enabled at any time in the server status window. If you have any queries regarding user modes please feel free to ask an operator on #solidirc.

Note: Modes are case-sensitive!

User Modes:

+B: Marks the user as a Bot on the network. A user with this mode enabled will show the line, “nickname is a Bot on SolidIRC” on a /whois. 
+d: A user with this mode enabled is considered ‘deaf’. The user will not receive any messages or notices at all. 
+I: Hides all channels the user is in on a /whois.
+R: A user with this mode enabled can only receive private messages from registered users.
+S: Strips colour codes from any messages to the user.