I couldn't find a format for this but, I think if we put floating nametags at some warps and spawns (wilderness, spawn, anywhere else that has directions) instead of signs people might pay more attention to rules plus, it would make the server look a little more appealing (not that it Isn't) If we put a nametag at spawn when players first join that tells them "Welcome to the DMU universe, please do /warp rules" or something like that people would most likely read it I think.

2 block height command: /summon ArmorStand ~ ~ ~ {Invisible:1b,CustomNameVisible:1b,CustomName:name}

1 block height command: /summon ArmorStand ~ ~ ~ {Invisible:1b,Small:1b,CustomNameVisible:1b,CustomName:what you want it to say}

The idea is nice, it would be useful to put up such tags at important warps.

These could be implemented via invisible and named armour stands, I remember that there are people who can produce such creations.

 Both commands placed in thread, all you would have to do is change the name

 Or it could be like in whoville when you join for the first time it forces you to read the rules