Proof of Time Travel
Google has a cool new feature: you can search every book they've digitized for a specific word or phrase, and then chart how often it appeared by year. I'm sure this will be invaluable to language historians, but I've discovered an even more important use: you can use it to search for time travelers.
For example, here's what the graph looks like for the word "Internet":
That's right: from the dawn of written language, up through the late 1970's, not a single human being in recorded history used the word "Internet"-- except a little flurry of people right around 1900. That clearly marks the chrononaut's first landing point in the time stream.
Now, imagine you are history's first time traveler. You wish to summon more of your ilk, to enjoy the wonders of the early 20th century. How might you contact them? Why, with your iPhone. Here's a chart of how often the word "iPhone" appeared in printed documents:
You'll notice a major spike in the mid 1940s, suggesting heavy time traveler presence during World War II.
In fact, once you start searching, the evidence is astounding, from the use of Google during the Civil War through the appearance of both "www" and "http" in 1902. But I will leave all that as an exercise to the reader.