I like to make sure that I put my name and phone number on the first page of each new notebook, especially if I'm taking that notebook with me or keeping it in my purse. That way if I lose it, the person who finds it can return it to me.
I don't often read my old journals, so I just keep them in a box labeled "Keep Out." You can keep them on a bookshelf, if you like. To make it easier to locate a specific journal later, you can write the date (or another identifier) on the spine using a permanent marker.