I just ask the tellers to check the large bills, 50’s and hundreds.

There are quite a few security features you can check like the watermark portrait on the right side of bill. Hold your bill up to a light. The micro printing on real bill is clean and crisp on a real bill. Counterfeits just don’t have the same feel as a real US bill. Rub your finger over the printing, a real bill has ridges on it, you can feel it better on the bust part of the portrait. It’s real distinctive. The yellow dots on the back are to prevent photocopying.