DNA may contain the message we're looking for. If you're familiar with SETI, the Search for ExtraTerrestrial Intelligence using radio waves, this article postulates that we need to be looking in the genetic code: DNA, the molecule that contains the script of life, encodes its data in a four-letter alphabet. This would be an ideal medium for storing a cosmic calling card. In many organisms, humans included, genes make up only a tiny fraction of their DNA. Much of the rest seems to be biological gobbledygook, often called "junk DNA". There is plenty of room there for ET to etch a molecular message without damaging any vital genetic functions.