The caretaker of a world may occasionally designate certain citizens to be Public Speakers (PS), who are citizens whose chat messages are transmitted to all users within a given area. Everyone in the area can hear and see a public speaker, regardless of how many other people are around. You can tell a Public Speaker by the fact that their chat messages appear in that chat window in bold text.
Since by default all users hear the nearest 50 users, the Public Speaker effect is only really useful in situations where there are more than 50 people gathered in a single location, such as very large gatherings and events.
If you encounter a public speaker in a world, remember that they can hear all the conversations going on around them, so be patient if he/she does not respond immediately to your questions. In really crowded areas it is can be quite difficult for a public speaker to hold individual conversations since there are so many people talking at once.
Public Speakers have access to additional special avatars which other citizens cannot use.