Paul Davies and Robert Wagner at Arizona State University have an interesting proposal: They want to use crowd-sourcing to search high resolution images of the lunar surface for evidence of extraterrestrial visits. Although they admit that the likelihood of actually finding something seems small, the cost of this sort of effort would also be extremely small, as almost all of the work would be done by interested volunteers.
For myself, I’m happy to see exo- and xeno-archaeology starting to receive serious consideration outside of the usual conspiracy theorist circles. I’ve long thought that if there are any advanced technological societies out there, it’s more likely that we will encounter evidence of their past activities than the beings themselves. The science of archaeology exists at all because artifacts so frequently outlast the people who create and use them. I can’t think of any reason to expect that to be different in space.