The idea of eternal inflation, with its attendant notion that we may inhabit just one of many 'pocket' universes, has raised many thorny questions as to how to test such a theory if cosmological and other observables are not uniquely determined. While these difficulties may not be insoluble, it is of great interest to search for directly observable signatures of such a 'multiverse'. I will discuss the possibility that collisions between neighboring bubble universes can leave observable signatures detectable by some or all observers inside them.