Feras Al-Jayoosi wore the clothing in Golders Green after the May Israel-Gaza conflict
He admitted four counts of wearing an article that supports a terrorist group at Westminster Magistrates’ Court on Friday.
The court heard that Al-Jayoosi’s T-shirts displayed the logos for Hamas’s Izz al-Din al-Qassem Brigades and Palestinian Islamic Jihad.
Both groups were proscribed as terrorist organisations by the British government in 2001, and were involved in the May Israel-Gaza conflict.
The outbreak of violence was linked to a rise in antisemitic hate crimes in Britain, at a time of waves of protest.
Three of the charges relate to al-Jayoosi wearing the T-shirts in Golders Green – an area of north London with a large Jewish population – on 8 and 9 June.
The fourth relates to an incident at Barbury Castle, an Iron Age hill fort in Wiltshire, on 30 May.
Al-Jayoosi, from Swindon, stood in the dock to confirm his name, date of birth and address before pleading guilty to the charges.
Chief Magistrate Paul Goldspring adjourned sentencing to 17 December for reports to be prepared.
“These are difficult cases to sentence,” he told the defendant.
“There is a fine line between support for a legitimate cause and support for a proscribed organisation and you have entered your pleas on that basis.”
He released Al-Jayoosi, who the court heard has been diagnosed with autism spectrum disorder, on conditional bail.
The case had been investigated by the Metropolitan Police’s Counter Terrorism Command.
Commander Richard Smith, who leads the unit, said: “Al-Jayoosi’s actions caused a great deal of concern within local communities, and an investigation was quickly launched as a result of a call to police.
“This case further underlines how important information from communities is to our work, and how seriously we take reports of this nature.
“I would urge anyone with concerns or suspicions about crime in their neighbourhood to call police – we will listen, and we will act.”
The Terrorism Act 2000 makes it illegal to wear an item of clothing in a public place that suggests they are a member or supporter of a terrorist group. The offence is punishable by a fine or a prison term of up to six months.
The British government has banned 77 groups under the same law, including Isis, al-Qaeda and other jihadist groups, as well as neo-Nazi and separatist organisations.
Additional reporting by PA