That's an impossible question to answer. But I'll take a stab at it.
They won't try to contact us directly at all. We will pick up some accidental evidence of them, like an artifact of their industrial activities, or some other collateral signal generated for purposes other than communication. We might pick up a signal intended for someone else.
For example, we might pick up emission from their asteroid defense radars, or notice the spectra of their industrial pollutants as they dump them into their star for disposal.
I'm not too optimistic. If they don't want to be discovered (the most likely scenario) I doubt they'll be clumsy enough to give themselves away accidentally.