I found, a couple of days ago, a giant pennus on my server spewing out the tip with a sign eat XXXX next to it. I just deleated it with the f7 tool. I agree it wasn't pretty and my server is a 18+ server so it realy didn't matter. Infact I though it kind of funny but it was crude and I removed it cause it was ugly more then anything. The way it was done was by blueprint and with blueprints you can lay down a lot of stuff real quick. The 1 that was on my server was hidden underwater so I had to go swimming to find it. Erase the problem not the server is all I am saying. You over reacted.
Haven't you ever bee told that the people that do this kind of thing think it is funny and get a kick out of your complaining and fussing. Clean the problem up and go about your business and don't give them the pleasure of them getting under your skin, is the best way to get back at them. Ruin there fun.
You can also install plugins like object protection that will tell you the names of the people who have placed these things. I check the 1 on my server and it was done before I installed my added security programs so it had been there for a while. I bet your's had too, especialy when you say you had 100 of them on your server. Remember it is better to delete 100 of these things then to delete the server with 500 builds and claims on it. You just piss your clientell off when you destroy there work from under them.