As Lhiggle suggested, go to the treasury website and download the Savings Bond wizard. (his link takes you to the download page). The Wizard is spreadsheet program that allows you to enter an inventory of bonds to track. It will update the rates and values of the bonds for you as well, which I can't promise Bloomberg would do accurately or on time. You're much better off going to the source for the face value instead of Bloomberg, which can be glitchy and unreliable (I used to work there). If you want to know if there's a market for any bonds you hold, then consider using Bloomberg (and be sure to have a shot of whiskey handy if you plan on using a terminal yourself)
If you are holding this savings bond in certificate form you may need to take it in to a brokerage office and see if they can research this. I used to hold both my Series 7 and Series 63 licenses and had to work on researching these type things. You often need to have access to a bloomberg machine. If the bonds are being held elsewhere (like the transfer agent) you can call there to find out the value. If these are government issued savings bonds you may be able to locate a government website that could help you find a value. I would suggest though that either you speak with a broker or even call your local library and see if they can help you research the bonds. Hope this helps some.