But they usually are told they're muted. Either by people who are on IRC, and their name is being dinged by the muted person, or the mods tell them.
Sim has it the way he has it for a reason. We don't want them to know that they are muted because the can just easily get on another account to start their spam etc. When a mod mutes someone, most of the time they are told. But, if someone is spamming, cursing or doing something they aren't supposed to, then they won't be told they're muted unless they ask. Lets say that player1 starts spamming, he then gets muted for spamming and the game tells him that, after that he makes another account to spam again. Now he spams all day by making new accounts and it's at a time that sim isn't on. Tell me, what can the mods do? They mute him, he makes another account. It will go on until sim bans the player, which may take a while or a short amount of time.