Looking for Matrioshka Objects? Intelligent Jupiters? Alien bases in the Oort Cloud? Dyson Spheres? Ring Worlds? Kardashev Type II Civilizations? Here’s some data for ya.
The only signature we can count on any ET sending out, regardless of their technology level, is waste heat. There is no way they can cloak this, the laws of Thermodynamics, and all that. And really big technological civilizations will generate a lot of it.
http://www.jpl.nasa.gov/news/news.cfm?release=2012-072&cid=release_2012-072
http://wise2.ipac.caltech.edu/docs/release/allsky/