It began the moment the Pope stepped on US soil. "Pope Francis scoots around DC in a humble Fiat," wrote USA Today. "Pope passes on limo for modest Fiat," echoed Fox News.

And after the news reports came the commentary. "Pope Francis and his little Fiat... don't think the world hasn't noticed," mused the New Yorker. "A Love Letter to the Fiat 500: The New Popemobile," appeared in Vogue. "The Pope, his black fiat and the symbolism behind it," was a headline on NPR.

Social media was awash with it too. "I want a Papal Fiat," tweeted @charlesthomas. "OK... I want a Fiat now... is that weird? LOL! PopeFiat!" said @LauraHarrisWFTS.

"For some reason unknown to me I kinda want a Fiat. #productplacement," was @griswoldkmtv's verdict.

There was also an instant spike in Google searches for Fiat, Fiat 500 and Fiat 500L, the model the Pope travelled in - five times more searches for the word "Fiat" on the day of the Pope's arrival than the day before and nine times as many searches for "Fiat 500".

Most of the searches were made in Washington DC, where the Pope started his US visit. The neighbouring states of Maryland and Virginia also featured highly, as did New York - where he went next - and California.

There may also have been an effect in showrooms.

"We sold one to a lady who had been looking at other cars. Last night she came in and said the Pope had convinced her," said Mark Cowdin, general sales manager at Safford Fiat of Tyson's Corner, which is about 10 miles outside central DC.

"We've also had several appointments made - people are calling and saying they want one of the Pope's Fiats. My guess is we'll sell two to three times as many as we normally do this month."

The Fiat 500L - larger than the classic 500 - sells for about $20,000 in the US. Cowdin says it is seen as an international, modest, family car, but is fun to drive and has a bit of personality.

Pope Francis is known for eschewing luxury cars for more humble rides.

His first ever papal visit was also in a Fiat, his popemobile in Cuba was a converted Peugeot, and he is renowned for being driven around in a Ford Focus in Italy. Back in Argentina he drove an ageing Renault 4, and he was given another one by a friend soon after moving to the Vatican.

The pontiff's choice of the Fiat for his US trip made "perfect sense", according to The Wall Street Journal's motoring journalist, Dan Neil.

"He's so charming and unaffected. It's the ultimate everyman car," he says.

"There's also a gentle nod to the Vatican and Italy, which shows the Pope is not above playing a little optics - I'm sure he and the CEO of Fiat have met."

The Fiat 500L doesn't make the list of the top 20 selling cars and trucks in the US. Pickup trucks and Japanese sedans dominate, according to the latest industry figures, with sales of trucks and SUVs said to be on the rise.

The Ford F-Series, Chevrolet Silverado and Ram 1500 were the three most popular in August, selling 71,332, 54,977 and 45,310 respectively. By contrast, only 350 Fiat 500Ls were sold in the US in August 2015, although Fiat sold 3,388 cars across all its brands.

The size of a Ford F engine varies between 2.7 and 5.0 litres. The Fiat 500L's, by contrast, is a mere 1.4 litres.

Cowdin says it will be interesting to see if there is a "Pope bump".

"If he can get atheists to watch an address by a Pope," he says, "he can probably move the sales needle."

(BBC)