VOICE

Usage: VOICE #<room> <nick>

This command will voice (+v) you in the room. You must be a VOP or higher to use this command in the selected room. Much like the op command. You must be an AOP or higher to voice someone else.

Example:
/msg chanserv voice #spiderslair Jenkins

This command is mostly useful for voicing yourself in rooms where you are a VOP. When voicing others you would generally just mode them +v, but you can use services if you wish. Being able to voice yourself with services means that you do not need to leave and rejoin the room to be revoiced.
Note: Service commands are deprecated, see the server command /HS VOICE for the new command.