I have some books that were part of a charity sale where the ladies marked the books with 2 or 3 letters on the edges (most on the bottom edge) so that it would be easy for them to ring up the different price groups.  I'm trying to see if they are postable here.  I read where ex-library books or bookcrossing books can have stamps or markings on the edges. can I assume that these are ok also? 

Writing onthe edges of the pages (ie: opposite the spine when the book is closed) is acceptable, it's no different than the stamps used by libraries. This has been asked frequently lately, I wonder what's up with that? Anyway, answer is yep, it is :)

thanks for your reply  sherry.  I'm glad because they are very good books besides that.  I did (very nicely) tell the older ladies when I was checking out that perhaps they could use a different way to price them,  but they said it was the easiest way for them to do thousands of books at a time....LOL, can''t really blame them.

I have some great books at local thrift stores in their 'value bin' at 10 for $1.49 and they always mark the spines with a line about an inch long in marker.  I suppose its an easy and quick way for them to see that the books are clearanced without having to spend time putting new price tags on them.  I'm happy we can post them here... I have found several wish listed books to post in those bins!!