You must be a UOP or higher to use this command in the room. This command will remove your (+v) voice status. If you are an AOP or higher you can devoice other people who do not outrank you.
/msg chanserv #spiderslair devoice Jenkins
This command is useful in rooms where voice is used to symbolize some level of ability in the room. Many help rooms will voice helpers who are still in training. If you are voiced but are going to be inactive you cannot simply mode yourself -v in the room, since only ops can set room modes. This command has services remove the voice for you. AOPs and higher can use services to devoice people who do not outrank them, but they can also just mode them -v normally. The services command would be useful if you are an AOP or higher, but not currently opped and want to devoice someone without having to op yourself first.