Human DNA = hazardous material
Putting our DNA on the moon is retarded:
If good aliens find it, they will have trouble to no end, given we are the most aggressive and unpleasant species this planet had the misfortune to be infested with. At least they should also put a warning beacon, telling any passers by to stay away from the moon in the name of their own safety.
If bad aliens find it, our DNA will enable them to design very specific weapons to eradicate us while preserving the planet for themselves.
So either way, its the idea of a nutter.