Merely stating that life is Intelligently Designed makes at least two predictions -- intelligence and design. In order for these predictions to have any meaning in the physical world, where we are unfortunately condemned to conduct the entirety of our investigation, the evidence must be physical. Otherwise, we may just as well call the Intelligent Designer by the name, God, and be done with it.
Because ID really is just a surrogate for the god of Genesis, the ID proponents generally don't care to make testable predictions. However, some have been made in the vain hope that they will pan out. Irreducible complexity is one such prediction. It depends largely on an argument to incredulity. They point to some complex organism, chemical pathway, appendage, etc. and pronounce it as irreducibly complex and therefore impossible to exist unless designed by a higher intelligence. Then some humble journeyman chemist or anatomist works out the details and explains the thing so everybody (with the possible exception of the ID guy) sees how really simple and reducible it actually is. This doesn't stop the ID guy from trying. Meanwhile everybody else has abandoned even investigating irreducible complexity claims from the little boys that cry "Wolf."
Can you name the physical evidence that we have in hand in which an Intelligent process has Designed DNA?