> I think the methodology of the paper is flawed. Why would a time traveller from the future be discussing "Comet ISON" or "Pope Francis"? According to Wikipedia, comet ISON wasn't ever bright enough to spot with the naked eye, and thus left no significant impact on humanity. It's obviously too early to decide if Pope Francis will leave a deep, significant impact, but odds are against it.
The problem is that they needed something to search for where we have a clear, well defined horizon before which people were extremely unlikely to mention the name at all.
Both of these meet the criteria because the names are now all over the historical record, but the names were new. In the case of Pope Francis, he was not only the first Pope Francis, but also the first pope in a millennium to pick an entirely new name (John Paul I was the first John Paul, but both John and Paul separately have a long history).
You are right that it might mean that they would miss time travellers. Who knows: If time travelling exists, all travellers might even be warned about this specific experiment.
But they in any case could not prove that we have not been visited by time travellers - all they could do was to pick terms that if they found them would give a strong indication that something odd was afoot.
They were also limited in that they were explicitly looking for something that could be researched cheaply, and by looking at the internet, and so an example like Hitler would not work.
> Identify "black swan" events (dot com crash, 2007 financial crash), and look at people who slowly offloaded their assets prior to it. Identify "underdogs" that became huge (eg. Apple in the 90s) and look at people who slowly brought into it during that period.
The problem is that you will likely find lots of people. People have all kinds of different reasons for investing, many of which leads to looking prescient after the fact.