It is a command that leaves a .txt message on the server, for example, some day a dedicated server is set. It has nothing but vanilla DM. So this person wants the server to enable the "3sec start invulnerability at spawn". As the server owner is sleeping at that time, he wants him to know it, or perhaps, about a bug, or some stuff like it, or some guy hacking. He can leave a:
-Public message: it is printed to every client, once, and also is sent to the server (l_pubmsg)
-Server message: It is printed to the client who sent it, and sent to the server, no one else will read it. (l_sermsg)
If this works, i'd be great for people who don't have a forum or stuff, and use the MOTD of q2admin to announce stuff.