We fire a sodium laser at our observation targets-
I get a kick out of imagining P'xpar, a grad student on his home planet of Gakzer, writing his thesis after discovering "anomalously high" sodium emissions from an otherwise unremarkable yellow star... 8^)

Totally impractical for our laser of course, but I DID do a calculation that showed that with our current tech it IS possible to be noticed by civilizations 10 LY away that have telescopes like ours...

Off hand, I would look for narrow-band emissions near 1.064 micron, .78 micron, or _possibly_ .512 micron or 10 micron... in that order, assuming our level of laser technology- other wavelengths are certainly possible...

One interesting way of sending a beacon to intelligence is to use you sun as a lighthouse- You could create a large amount of technetium, (an artificially made element), and dump it into our sun- any race that notices the spectral lines of an artificial element in our suns spectrum would definitely take a second look