Image copyright AFP/Getty Images Image caption The symbol started to appear on Tom Steyer's hand in late 2017. He's not the only person to adopt it.

In between the frontrunners during the Democratic debate on Tuesday stood Tom Steyer. You might have spotted him: he was the candidate caught in the middle as Bernie Sanders and Elizabeth Warren clashed off-mic at the end.

It was the most intriguing moment of the debate, but if you looked closer, you might have been intrigued even further.

On Mr Steyer's left hand was a symbol, crudely drawn in pen: one large cross with a smaller cross in each quadrant.

It was not the first time the billionaire hedge-fund manager has been seen with it in public - he's drawn it every day for at least two years - but this debate introduced the symbol to a new audience once again.

What is the symbol?

A symbol with five crosses like this is known as a Jerusalem Cross, and it was employed as the symbol of the Kingdom of Jerusalem from the 13th Century. The kingdom was established by crusading European Christians who invaded and conquered Muslim lands.

There is not one agreed meaning to the five crosses - various theories suggest they could represent Christ and the four gospels, five wounds suffered by Christ on the cross, or the four points of the compass.

Image copyright Getty Images Image caption The Jerusalem Cross seen at the entrance to a Franciscan convent in Jerusalem

The original symbol is likely to pre-date even the Kingdom of Jerusalem and was used in feudal states in what is now the country of Georgia, which since 2004 has used the five crosses on its national flag.

Why does Tom Steyer use it?

In an interview with BuzzFeed last year, before he announced he would run for president, Mr Steyer was asked about the significance of the cross on his hand.

"It means to tell the truth no matter what the cost is," he said. "For a while now, I have drawn it on my hand every day to remind myself to always tell the truth. I later discovered that it has traditionally been known as a Jerusalem cross."

Image caption Tom Steyer in a BBC interview in June 2019 - with the mark on his hand

He appears to have started drawing the symbol in the winter of 2017, and in May 2018, he told Politico it was a reminder to always tell the truth, even if you are put on the cross for it.

He also said it was the international sign of humility, although this is not established as a thing.

Mr Steyer - a long-term Democratic donor - is Christian, and this month told a podcast that he was 30 when he found God. But he has not drawn a link between his faith and the symbol on his hand.

Instead, his drive to "tell the truth" is tied to a political group he launched in October 2017, named Need to Impeach, that focused on removing President Donald Trump from office.

It's a message the 62-year-old has repeated since entering the race for the presidency last July. He has also condemned corporate interests that affect government policy, and vowed to declare a state of climate emergency on day one of his presidency, were he to be elected.

Who else uses it?

In recent years, images and terms associated with the Crusades in the Middle East have been appropriated by white supremacists.

When a white supremacist shot dead 50 people in mosques in Christchurch in New Zealand in March last year, his so-called manifesto was reported to include references to the Crusades.

Image copyright NurPhoto via Getty Image caption White supremacists marched in Charlottesville, Virginia, in 2017, where an altered Jerusalem Cross was seen (far right)

Banners depicting the Jerusalem Cross, along with the term "Deus vult" (God wills it) that was associated with the Crusaders, were deployed by the far-right during a violent rally in Charlottesville, Virginia, in 2017.

As yet, however, the Jerusalem Cross has not been listed as a hate symbol by the influential Anti-Defamation League.

Last week, the US president's son, Donald Trump Jr, defended posting a photo of himself holding a rifle (known as a "Crusader") that featured a Jerusalem Cross - as well as an image of Hillary Clinton in jail.

The photo - posted days after the US assassinated Iranian general Qasem Soleimani - was consistent with a tradition among gun owners of "depicting various historical warriors", Mr Trump Jr's spokesman told the Washington Post. The company that produced the rifle said it was "objectively silly" to suggest the cross was a hate symbol.

"As with all symbols, context is everything," said Dan Jones, a historian and author of Crusaders: The Epic History of the Wars for the Holy Lands.

Jones himself has a tattoo of the Jerusalem Cross on his wrist. He received it a few years ago in Jerusalem, copying a technique used by pilgrims hundreds of years ago.

Image copyright Dan Jones Image caption Historian Dan Jones has a tattoo of the Jerusalem Cross

"In the context of a Christian pilgrimage to Jerusalem, this would have been a symbol of peaceful worship," Jones said.

"But in the context of Donald Trump Jr with a Jerusalem Cross on the side of an AR-15 rifle, the context is very clearly one of violence - anti-Muslim violence - and of a civilisational clash going back to the Middle Ages."

The fact the cross has different meanings, like the swastika before it, means any presidential candidate should be more cautious about using it, Jones said, as appropriation of such symbols could play into the hands of those who consider the US to be aggressors.

"[Tom Steyer] clearly has his own reasons for scribbling it on his hand," Jones said. "But he has to be aware of the other context. Were he to be elected president, then Isis propaganda would be calling him the Crusader-in-chief."

Such a development is unlikely, however. As the Democrats enter primary season, the polls put Mr Steyer far down the list of favourites for the Democratic nomination.

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