The paper discusses the possibility of searching indirect ETI evidence using the images taken from the Lunar Reconnaissance Orbiter (LRO).
The authors begin by arguing the advantages of searching for ETI on the Moon. First, the Moon is very close to the Earth, so we could observe the features on the Moon in detail. Second, the surface of the Moon is rarely changed due to the low impact rate from meteorites. Therefore, any large artifacts left by ETI on the Moon should preserve for a quite long time for us to search.
Then the authors classify the kind of artifacts into four categories: 1) messages 2) scientific instruments 3) trash 4) geo-engineering structures. For messages, the authors argue that the chance of finding such messages on the surface might be low. Further recovery of such message might depend on radar technology or excavation. For scientific instruments, the authors argue that it might be worthwhile to look for solar panels at the poles of the Moon but LRO did not find anything. As for trash and geo-engineering structures, the authors suggest future excavation missions might find interesting features.
Finally, the authors discuss how they would carry out the search using the existing data base. First, they suggest either hiring people to examine the images or do a computer automated scan. The problem with computer automation is that it could only find specific features. But we could expect any kind of strange features from ETI.