We research all brands listed and may earn a fee from our partners. Research and financial considerations may influence how brands are displayed. Not all brands are included. Learn more.

Pope Francis Visits Roman Parish of Sacro Cuore di Gesu'
Pope Francis signs an autograph as he visits Roman Parish of Sacro Cuore di Gesu on January 19, 2014.
Origlia, Franco—Getty Images

"Cool Pope" Francis's popularity is clearly high. He has 7.21 million followers on Twitter. Entrepreneurs have rolled on a zillion pope-related gifts and collectibles to sell in celebration of his visit to America. His visit to the U.S. this week has is even delaying the iPhone 6s release in ZIP codes he touches.

But the reason you know he's made it big? There's a huge market for his John Hancock.

Pope autograph values have been trending up lately, with examples on eBay selling for around $1,800. As of Tuesday afternoon, a little bit after the Pope's arrival in Washington, nine people were watching this one listed at $2,350, and Pope Francis is now on a preeminent top 40 list of sought-after autographs, right up there with Fidel Castro and Prince William.

Even though the papal autograph supply is likely to increase as Pope Francis begins his six-day sojourn through Washington, New York, and Philadelphia, the influx is unlikely to be great enough to saturate the market and deflate autograph value—the 78-year-old doesn't just doesn't have a celebrity's schedule to sign stuff. In fact, the buzz from his trip could increase demand.

But signed pictures are nothing compared to the actual religious paraphernalia. Last year a papal skull cap went for $113,210 on eBay. And crazier still, a Harley-Davidson presented to Francis was auctioned for $325,924. He may not be able to turn water into wine, but he can clearly add exponential value to stuff just by touching it.

Experts, however, do warn against buying collectibles for the purpose of making a profit off it in the future. This stuff rarely holds its value or appreciates, so buyers probably shouldn't treat collectibles like investments. Even holy ones.

Read Next: The Pope's Retirement Package Is Better Than Yours