I have added a /warn <target> <message> command to the server, moderators and above have access. These warnings are not meant to be a permanent tarnish on your record, more of a way for staff to keep track of what you've done that day. They do not save when the serve restarts, staff has access to logs of both all warnings placed as well as player specific now from the log menu.
Also should be noted that the warning message that displays in the chat can only be viewed by staff members.