When you find the modern-day pen pal circles, it seems like you've found a whole new world, with its own practices and language. You'll get a friendship book with a bunch of strange acronyms after people's names, or people will talk about things that can boggle the average person.
The inside of a deco can look like this:
To the average uninitiated person, this can look an awful lot like gibberish. Let me try to explain:
FOR AND BY: means that the book was made for (name) by (someone else). If they're together, as in on this one (for and by), it's been made BY me, and will come back TO me when it's full.
THE LIST OF UNRELATED THINGS: usually, someone will put in what their interests are, ranging from activities to types of music. This is so you can look through the book and find people just like you (or different from you) to correspond with, and tells you a little bit about the maker.
THE ACRONYMS: This is where it can get complicated. There are tons of acronyms that all mean different things, depending on what kind of letters the maker/signer wants to get.
AA: answer all
AM: will answer most
SNNP, or NNP: No new pals, or Sorry, no new pals.
NM/NP: No men/No prisoners
LLP: Long letters preferred
ICR: Literally, "I can return", meaning that if you're the last signer, and you don't want to send it to the person the book's made FOR, but you don't mind sending it to the person who made it, they can return the book to the owner for you.
NPW/NSW: New Pals Wanted or New Swaps Wanted
WW: usually means "world-wide", or international pals OK.
Just to reiterate, an FB is just for addresses, whereas a deco is where you decorate a page and send it on.
There are also a few other types of books that seem to be less common in the circles I've seen:
lyrix: where you decorate a page with the lyrics to a song.
slams: where there's a question on each page that you answer.
quotez: much like lyrix, only with quotes.
sticker slams: where you put a particular type of sticker on each page.
I've also seen things like poetry slams, where you add the next line of a poem, though the ones I've seen haven't worked so well.
There are more acronyms than this -- as I see them, I'll post updates here.