Arnold Schwarzenegger was detained at Munich airport due to common travel mistake

Anyone who has flown internationally is likely to have noticed the red or green signs above the exit doors one passes through after picking up bags from the luggage carousel.

The green "nothing to declare" is the one used by most travelers (there's even a 2010 movie about life on the France-Belgium border of the same title) but those traveling with anything from commercial goods and food to excessive amounts of cash and other expensive goods need to declare what they are bringing into the country to customs.

Related: These Are the Worst Days and Times to go Through Airport Customs

While he is no stranger to crossing borders, actor and former California governor Arnold Schwarzenegger recently ran afoul of EU customs after arriving at Munich International Airport from Los Angeles.

Schwarzenegger's luxury watch got him detained (here's how much it costs)

As initially reported by CNN, Schwarzenegger was on his way to a charity auction in Austria in which he planned to auction off a luxury Audemars Piguet watch worth approximately €26,000 (approximately $28,280 USD) for charity.

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Schwarzengger was stopped for a routine check and found to have failed to properly declare the watch he was bringing into the country. He was held for over two hours and eventually released after paying the taxes required for bringing in a product of this worth into the country.

"He did not declare a product; a product that was imported from non-EU countries in order to remain in the EU and the process applies to everyone," Munich Customs spokesperson Thomas Meister told CNN in a statement.

Sources who were close to Schwarzenegger and communicating with him during the process at the airport told media outlets that he was not handed a customs card when passing out of the airport and immediately offered to pay the necessary customs only to have the ATM to which he was brought to take out the cash not work due to having a limit on how much one can withdraw at a time. Due to the late hour, a worker was also not around to repair it.

'A total comedy of errors that would make a very funny cop movie...'

Eventually, someone brought over a credit card machine and Schwarzenegger was able to make the payment and go on his way to Austria.

"Arnold was detained for three hours today at Munich airport for traveling with a watch he owns, that he might be auctioning at his charity auction tomorrow in Kitzbuhel," the source explained to CNN. "He cooperated at every step even though it was an incompetent shakedown, a total comedy of errors that would make a very funny cop movie."

The European Union requires those coming into the countries that are part of it to declare and pay tax on any goods valued at more than €430 (roughly $467 USD). The U.S. has similar laws for goods costing more than $200, $800 or $1,600 while the exact threshold will depend on the countries visited and how long one has spent out of the country.

Whether due to not knowing the law or to avoid the tax, not declaring them can subject one to heavy fines and even criminal prosecution.