User blog comment:TheDoctor230/How Would You Like To See These Show's End/@comment-34179759-20180105005101/@comment-34179759-20180108090114

@Ninja72, it wasn't from the crossover, it was from the episode Shogun.

On the 2056 story, Barry could've seen The Waverider in one his time travels and decided to warn Rip by sending him a message.