I'm often asked if there's a good book for interpreting the meanings of treasure symbols. While there are countless books on the market that claim to show such things most are just recycled from other books. The authors may have never seen the signs used in the field to verify their authenticity. I was once told there's more money to be made writing about treasure than there is hunting for it. I believe this holds true. If someone is trying to sell you a book about treasure signs then the odds are they're not finding treasure themselves.
There isn't a book that I can recommend as the single source for sign reading but there are a few books that will go a long way in helping you learn to read the signs for yourself. I highly recommend The Rocks Begin to Speak by Lavan Martineau. While this book covers how to read Native American pictographs the same process can be used for treasure signs. Especially when dealing with stacked or grouped symbols. Many of the Native symbols have been incorporated by other groups to be used as treasure symbols.
A safe bet would be that 99% of the treasure signs you come across are giving you one of three things. #1 is direction of travel. #2 the topography that you need to look for. #3 the layout of the treasure site. This is fairly universal among all groups. In our area you will often find symbols from the Spanish/Mexican and 19th century outlaws in the same area. What is a good area for one group is often good for others even if separated by a century or more in time.
I have spent countless hours researching and working in the field to understand what the signs and symbols are conveying. Hundreds of people over the years have sent pictures of symbols requesting help interpreting them. The majority of them I've been able to help with. My main effort is to help people to help themselves. You learn far more having to work out what a sign means on your own, with just a little guidance, than you ever will just being given the answer.
There will be a naysayer or two at my abilities to read signs but that is to be expected when you have so many armchair experts and book hustlers. Feel free to contact me for help. Unlike many others I'm not interested in knowing where your site is or charge a fee for help.
Good luck and good hunting!