Mr Jarrar's black cotton T-shirt bore the slogan ['We will not be silent.'] in both Arabic and English. He said he had cleared security at John F Kennedy airport for a flight back to his home in California when he was approached by two men who wanted to check his ID and boarding pass. Mr Jarrar said he was told a number of passengers had complained about his T-shirt - apparently concerned at what the Arabic phrase meant - and asked him to remove it. ... After a difficult exchange with airline staff, Mr Jarrar was persuaded to wear another T-shirt bought for him at the airport shop.
(HT: RELEVANT's Daily Slices, 31/8/06)
So according to the BBC the problem was that passengers didn't know what the Arabic text said, and were concerned it was something 'bad'. It would be disingenuous of me to ask if they would have been concerned if the text was in Greek, or Cyrillic characters, but this does leave me not knowing whether to laugh or cry.