The most reliable method of determining if a 1934 dollar bill is real is to look for tiny red and blue threads. Bills from 1934 lack many of the sophisticated anti-counterfeit measures present in newer bills, making the threads important for counterfeit detection. They are difficult to see without a magnifying glass, and are clearly fibers embedded in the paper, not markings drawn on the surface.
Another technique of vetting a 1934 dollar bill is to look for features that were not included on bills from that era. For example, all bills printed after 1963 bear the phrase, "In God we trust." Authentic bills printed in 1934 do not contain those words.
Modern dollar bills have many security features designed to foil counterfeiters. For example, elaborate microprinting and metallic security threads are standard features on most bills. The tiny designs printed on real Federal Reserve notes have distinct edges and are not blurry, faded or smudged. On counterfeit bills, these designs often have fuzzy edges, and the presidential portraits lack sharp contrast between the faces and backgrounds.
Another popular method of counterfeit detection is examining bills under ultraviolet lamps. This reveals the presence of otherwise invisible ultraviolet ink. This method is popular in nightclubs, bars and other establishments where low lighting conditions preclude many other visual detection methods.