I've been hearing claims that when players type /nearby and a disappeared mod is close, it shows their name and that when typing in local and a disappeared mod is close, it does not say "No one hears you." I decided to test this for myself to see if there is any way for a player to tell if a disappeared mod is nearby. Here are my results:
/Nearby gives the name: FALSE. Even though a disappeared mod was standing right next to me, /nearby still said "None!"
Chatting in local doesn't say "No one hears you": TRUE. With a disappeared mod standing right next to me, saying a line in local chat did not say "No one hears you." It said nothing, meaning that another player received the message.
Conclusion: This is a problem. Disappeared mods should not be able to be detected in any way, especially by players trying to avoid the law. Since there is a way for disappeared mods to be detected, this means that griefers could type lines into local chat and skedaddle when "No one hears you" doesn't show up. I believe this should be fixed as soon as possible to make moderation more effective.
Special thanks to Kodak28 for helping me with the test.