Carrying a bucket of cement and a heavy bronze plaque, Ekachai Hongkangwan set out across Bangkok's heavily-policed Royal Plaza in late June to perform a solo act of DIY dissent. But the 42-year-old was quickly bundled into a police van before he could lay down the metal disc -- an exact replica of a monument that was mysteriously removed in April, sparking fears officials were trying to whitewash history. The 15 inch (38 cm) plaque, which had lain undisturbed for decades, marked the bloodless 1932 Siamese Revolution that ended absolute monarchy. But it was suddenly replaced with a new plaque espousing loyalty to Thailand's royal family, an institution whose influence has roared back into prominence in recent decades as democracy has faltered. The date Ekachai chose for his one man protest was 24 June, the anniversary of that revolution. "I wanted to dig the new one out but I think (knew) it will be very difficult for me," he told AFP from his house in eastern Bangkok, a wry smile across his face. The attempted restoration was a dangerous and rare act of subversion in a country smothered by an arch-royalist military and where criticism of the monarchy is being purged at an unprecedented rate. More than 100 people have been charged with Thailand's notorious lese majeste law since the junta's 2014 coup, threatened with up to 15-years in jail for each slight to the country's royals. - Unprecedented purge - Record-breaking, decades-long sentences have been handed down and many of those advocating for reform of the law or pushing for greater scrutiny of the royals have gone to ground, fled or been imprisoned. Ekachai, a former lottery ticket seller, served nearly three years for the offence in 2011. His crime was selling Thai translations of State Department cables and international press reports that were unflattering of the then Crown Prince and now King Maha Vajiralongkorn. Since his release Ekachai stayed away from protest, choosing instead to set up a small foundation to help those charged with lese majeste. But the disappearance of the plaque reignited his defiance. "This is a democracy symbol," he said, proudly retrieving the replica plaque from the back of his house, which authorities returned after he was released without charge for his stunt. "They try to make it a hidden history." Junta officials and police have said they do not know what happened to the original plaque, a position that stretches credulity given it lay outside a palace in a heavily policed area of the city. CCTV cameras were not working when the plaque vanished and authorities have warned against further protests or enquiries over the mystery. Thitinan Pongsudhirak, a politics expert at Chulalongkorn University, described the plaque as "a bump on the road of Thailand's royalist narrative". Until its removal few knew it existed "even those who live in Bangkok." "But now its controversial disappearance has led to a kind of rebirth of the June 1932 political change from absolutism to constitutional rule," he told AFP. - A history lesson - So far Ekachai has managed to avoid being charged over the plaque and he steers clear of any direct criticism of Thailand's royals. Instead he focuses on trying to reform the lese majeste law, which makes scrutiny of the family impossible and forces media to self-censor. It was during the last few decades of King Bhumibol's 70-year reign that the law was increasingly wielded, despite an address the late monarch gave in 2005 saying he was not above criticism. Since Bhumibol's death in October little has changed under Vajiralongkorn, who has yet to attain his father's widespread popularity. At least eight people are known to have been charged with lese majeste charges since his succession. One case expected to hit the courts soon involves a man charged for liking a sarcastic Facebook post about Bhumibol's favourite dog. "I'm not opposed to the monarchy," Ekachai said, a portrait of the recently departed King Bhumibol Adulyadej hanging behind him. "But that doesn't mean we should be unable to criticise them at all," he said. While Ekachai admits his plaque replacement stunt was never going to succeed, he dismisses those who say such acts are futile. Following his detention he discovered his military interrogator was unaware that the date he had chosen marked the anniversary of the 1932 revolution. "In school they teach them nothing about this, they try to erase it from history," he said. Breaking into a chuckle, Ekachai said he was delighted to get a chance to give the officer a brief lesson.