Blue stamp? I'm assuming you mean that the serial code and a few other things are in blue. If so that means you have what is called a "Silver Certificate" Silver Certificates (which has red or blue writing on them printed through the Treasury Dept which says something like "this bill is exchangeable for an amount of silver) are getting rare enough to where they are worth more than the amount printed on them. A 1935e silver certificate (I believe has blue on it) can be worth a lot or nothing at all depending on the wear and tear it has and the current market. If there has been a flood of 1935e in mint condition then any bill that has been folded or soiled will be worth nearly nothing more than the dollar amount on it. http://www.ingrimayne.com/econ/Banking/Silver.html has two banknotes the "blue" lettering one and the green lettering one. The blue is a silver certificate, the green is a modern worthless dollar (nothing backs modern dollars) http://web.bsu.edu/kparker/givan/essays_maui1.asp Has one with red lettering (you will need to scroll down a bit). Mind there are different series, like the 1935e there are others like the 1935d. The value of any collectible currency is usually based on its condition, if the bill has gone through the washer several times, been the rope in a tug of war, has been folded and spindled a lot it is worth far less than one which was gotten fresh from the mint and stuck in a book to where it is in "mint" condition. You can take it to a coin collector and get it assessed. If they think you are going to sell it to them they will way underestimate its value. If you make it clear that you are just curious about it and have no intention of selling it in the near future they will give you a better estimate. Further they may tell you how to preserve it so it can maintain and even grow in value as time wears on.