When I say "advertise" I'm talking through chat so people know that the !warden command exists on our server. Some player's may already have a !warden command on their "main" server and try it without needing an advert but not every new player will.
I can't speak on the nitty gritty of plugin/code building but it really is unnecessary. Maybe not to you as you don't have experience with it (not a diss) but rarely is there a time when there are so few people w mics or server knowledge on JB that will make this a necessity. This is also an opportunity for our player's that are looking to do more (helping new players), to get their foot in the door.
When making an advert for it in chat, what would it say without it being "!warden will show you that there is no warden" or something similar. The adverts give a quick description of the command so player's know when to use it, it'll have a description that'll show the command useless. If anything just have a quick prompt when you load in saying "play ct if you'd like to be a guard // *no warden*".
I love that you're looking for new ways to improve the server but just being honest, this isn't the one in my eye's. Most of our Admin applicant's come from JB and I'm gonna use this as a little shout-out but just yesterday with this same situation, a new player asked if there was a warden and @DabOfGravy answered him quicker then I could.
A !warden command will be created & implemented just for it to be useless, so that's why I say it's unnecessary when there are other quicker & less time consuming way's of achieving the same goal.