I will discuss the theory and observational signatures of a cosmic wake from a cosmological bubble collision. I will show that bubble collisions lead to distinctive signals in observables such as the cosmic microwave background temperature and polarization. The predicted polarization pattern has distinctive features that when correlated with the corresponding temperature pattern are a unique and striking signal of a bubble collision of extra-universal origin. These features are the first verifiable prediction of the multiverse paradigm and lie within the detectable range of current experiments such as Planck and future polarization missions, giving us the potential to confirm the existence of the multiverse, and bolster the idea of the string landscape in the near future.