A better known test was done in 1942 during World War II to test alternative types of paper. This was a precautionary measure in case the current type of paper supply could not be maintained. Series 1935A notes made of the special paper and were printed with a red "S" to the right of the treasury seal, while notes of the control group were printed with a red R. Because they have some collector value, fake red S's and R's have been applied to regular Series 1935A notes to try to pass them at a higher value; checking a note's serial numbers can prevent this. Serial numbers of the R group range from S70884001C to S72068000C and serial numbers of the S group range from S73884001C to S75068000C.
