The poppy stamps shown are not actual stamps issued by the US postal services as they don't have a value or the country of issue written on them.
David Caruso and Esai Morales were both on NYPD Blue (1993). Caruso played Det. John Kelly and Morales played Lt. Tony Rodriguez.
The letters sent to each CSI are parts of an overall picture; a jigsaw puzzle. They put all the pieces on a table and sorted the pieces manually into place. Interesting that they didn't scan the pieces and use a computer to arrange them. They use computers for almost everything else.