As stated above, when WIMPs interact with other WIMPs they annihilate each other and form neutrinos, electrons, positrons, and gamma rays. The very interesting thing about WIMP annihilation and their products is that the muons, from WIMPs’ neutrons decaying into muons, end up getting pilled up in the centers of large objects such as Earth, the Sun, and the center of the Milky Way. This especially happens in the Earth because the neutrinos coming from WIMP annihilation interact with the rock in Earth’s interior and produce muons that carry WIMP signatures. This means, that you can use the Earth as a shield for cosmic muons because you want to observe the ones coming from the interior of the Earth, not falling into the Earth. The muons that are pilled up inside the Earth end up radiating up through the Earth. This is very important because we can conduct experiments showing which direction the muons are coming from. So far, nothing has been found, but astronomers and physicists are extremely hopeful. (4, 6)
Another possible indirect detection is to study the gamma rays produced from WIMP annihilation. These gamma rays would produce a unique spectrum that can be traced back to WIMP annihilation and even find the mass of both WIMPs! There are some promising experiments looking for this “gamma ray shower”. If we can find both muons and the gamma rays, that would prove the existence of WIMPs! (4, 6)