This may seem like a dumb question, but hey...I'm kinda new!

I usually buy books by the box full, and as I read them I take a highlighter and put a dot on the first page of the book, so that I know I've already read that one. Are these books ok to swap?

Thanks.

What do you mean by "first page"?.  The first page of text, or the flyleaf?

If it is the first page of text, that MAY be considered underlining for which you would need to follow the textbook rule.

If it is a nontext page, then it would be fine.

"Books by the box full."  You're a woman after my own heart.  Welcome!

Invest in some cheapie sticky notes and slap one on the cover or first page when you've read it.  No more questionable postability.  :)

Usually the flyleaf, sometimes not.

I never thought of using a sticky note...

Putting our little mark on the book is what my family (a very large family) always did when passing around books to read...that way you would know who read it, and who hadn't...and that way if it was a really good book, you wouldn't ruin it for someone who hadn't read it by talking about the good parts!! This was also our method of knowing who to pass it on to. 

Now that I live so far from family, and aren't able to borrow books from them, I generally by them by the box full at garage sales, flea markets, auctions, etc...I can't tell you when the last time that I bought a NEW book...just can't force myself to spend 8+ dollars on a book, when I can get a couple of boxes for that!! lol

Welcome to PBS and the forums Christina!

Not a dumb question at all.  A small mark inside the cover isn't unpostable, but anything on a text page is and could only to be posted using the Textbook Clause. 

Post-it's are a good option, or even just a small pencil mark you could erase before mailing to another PBS member.

I make small marks on the inside of the back cover. It's OK to post.

I've seen a lot of people post about the "textbook clause". What exactly does that mean?

Christina, see this page: 

http://www.paperbackswap.com/help/search.php?terms=textbook

I used to always put a small highlighter dot or small slash on the outside edge of paperbacks when I read them. That was postable as it was similar to a remainder mark. 

I was going to suggest what Melanie said, put a slash on the side like a remainder mark.  Years ago I inherited a large collection of murder mysteries from my stepmother.  She had a habit of writing the year on the binding in marker.  Not super big but noticeable and they were postable here.  She would put something like '97 or '01 or something, I'm assuming so that when they were on her bookshelf she could see when she had read the book or something. 

Marks that are on the side, the edges of pages, can be easily removed with a piece of sandpaper.  Hold the book firmly while sanding the edge.  

great ideas...thank you all

My sister keeps a notebook listing the books she owns, and she puts a checkmark by the ones she's read.  I'm a little more techie.  I have a computer program that does everything for me (lists the book, author, all info, if I've read it, etc.).  But the notebook would be pretty easy to do.  Just another suggestion...