From Centauri Dreams.
An alien artifact may be worth many signals in terms of understanding the artifact or signal's originators, or even detecting it against background. If self-replicating (von Neumann) probes are possible, we should expect to see self-replicating artifacts first.
Paul Glister takes the replicator question into account in this post, and goes into a discussion of how the replicators would communicate with each other - so we can detect them. This begs the same question. Why do we assume the replicators are communicating with each other, or with their originators? There are good reasons to think that the replicators we would eventually see are the most fertile ones - the ones that have mutated to maximize their own spread, at the possible expense of all other features - and it seems that communication, seen in this light, is an energy-wasting luxury. In this view, an argument can be made that they might want a way to detect whether a star system had already been colonized (or overpopulated) so they could aim for an as-yet unplundered one, if they're more than just interstellar dandelion seeds.