Thomas Edison Signed Letter. Auto Graded PSA Mint 9The Great Inventor! Offered here is an exceptional letter signed by Thomas A. Edison, the most influential inventor in American history! Penned on his official Laboratory of Thomas A. Edison, Orange, NJ letterhead, Edison has signed his name in bold black fountain ink, displaying his iconic umbrella style signature with the T stretching dramatically across the entire autograph one of the most recognizable and desirable signatures in the hobby. Dated