Hi its my first post and would like to get some info..A friend of mine bought a 1991 20 dollar bill in 1994 from an auction that has no optical security device (OSD)which is the little square foil on the top left of the bills...It is uncirculated...He told me that no other bill like his has been on the market as a 20 dollar bill but heard there was a few 50 dollar bills that had that same error from the printing company...He is interested in selling it and I am interested in buying it for myself...I have searched everywhere and could not find any info on those type of errors so I could get a ball park figure on the price of it...I could not even find a 50 dollar bill with that type of error on it or a 100 dollar bill...He is not asking a low price on it so thats why I need help to know more about this type of bill...Any info on this would be nice...Thank you and thanks for having me on this forum