People vs. Persons: Sometimes of Interest

Why the supercool TV show poster, you ask? It's there because I received the following e-mail from Lori:

I found your blog and I love it. Since you are good at clarifying which words to use, could you explain 'persons'. When I was in school and learning about plural words it was 'person' and 'people'. It was drilled into my head. I hear newscasters and others say 'persons'. That irks me to hear that. It doesn't sound right to me. When did 'persons' become correct?
 

As Lori and millions of schoolkids know, people is the plural of person. Duh. But English is a nutty language, where old-school ways can die hard. There are times when persons is the better, or at least the more conventional, choice.

Back in olden times—and I mean way back—persons was the plural form of person.  And in legal settings today, persons is still used as a synonym for 'individuals'. A TV newscaster might report that police are searching for a 'person of interest' in an investigation. In this sense, they are looking for an individual. In its plural form, the phrase becomes 'persons of interest.'

Legal documents often contain the phrase 'a person or persons' instead of the far less clumsy 'one or more people.' Both phrases mean the same thing, but 'a person or persons' is the convention. This is one reason why legal documents are so excruciating to read. And it might even begin to explain why lawyers are so unpopular.

Quick rules:

• Use people to convey the collective sense of a group. There are a lot of people in the auditorium. 
• To stress that you are talking about individuals, it is sometimes acceptable to use persons (but never in everyday conversation or you'll sound like a tool).
• In legal settings, persons is regularly used instead of 'individuals'.

Flash assignment: In an elevator, there is often a sign stipulating the maximum number of individuals allowed inside. Does it say persons or people? (Bonus points to anyone who can send me a photo of such a sign! Get your cameras ready!)