The Metropolitan Police Bureau has warned the Progressive Movement could face legal action if its members are found guilty of being behind the laser projection of "seek the truth" on landmarks in the capital over the weekend.
The message is linked to red-shirt protests in 2010 and the phrase is considered an anti-government message by the MPB.
It was projected onto the Democracy Monument, a BTS Skytrain station and a wall of Wat Pathum Wanaram on Sunday night.
Six people were killed inside the temple, located near Siam BTS station, when soldiers were ordered to disperse a months-long street rally by protesters against the Abhisit Vejjajiva government.
The Progressive Movement group has claimed responsibility for reviving the political message and police have launched an investigation into the matter. The group was co-founded by Thanathorn Juangroongruangkit, who led the Future Forward Party before it was disbanded by the Constitutional Court in February over a loan controversy.
MPB commissioner Pol Lt Gen Phukphong Phongpetra yesterday said police will act against the group and they are waiting to receive a complaint about the laser projection because the message was beamed onto privately-owned buildings.
He said the projections may have disturbed people. "Police are also gathering evidence to find whether the message caused damage to private individuals or organisations," Pol Lt Gen Phukphong said.
He said the authorities understand people's right to freedom of expression, but people have to watch what they express. Pol Lt Gen Phukphong said any message that "distorts the facts" may lead to legal action. No one has been charged in connection with the laser projections so far.
Anulak Chenthawanit, a red-shirt member, was arrested for allegedly defying the emergency decree after he held political activities near Silom subway station, where Gen Kattiya Sawasdiphol, a supporter, was killed during the protests.
Sathit Wongnongtoey, a Democrat Party MP for Trang, questioned the motive behind the laser campaign.
Mr Sathit on Facebook said it was a "new trick" by anti-government groups to spur a mass protest after political gatherings were halted earlier this year due to Covid-19.