Law enforcement officers are investigating who supplied calendars bearing pictures of former premiers Thaksin Shinawatra and his sister, Yingluck, which are now being distributed in some regions, according to deputy national police chief Srivara Ransibrahmanakul.
More than two million of the calendars are said to have been published, with many distributed in Bangkok, the Northeast and the North.
Pol Gen Srivara said no evidence has been found yet to pinpoint who was behind the distribution.
The calendars were distributed at Thammasat University, the Constitutional Court and areas in Ubon Ratchathani and Udon Thani, he said.
Security and police officers are investigating, Pol Gen Srivara said, though he noted it was unlikely the two former prime ministers, who are both in self-exile abroad, were responsible.
"This is unlikely to spark political conflict," said Pol Gen Srivara, adding attempts had been made to distribute similar calendars before.
Referring to security officers who were sent to check where the calendars were stored, Prime Minister Prayut Chan-o-cha said officers would be on the lookout for any issues that could trigger hate crimes.
Both of the former prime ministers have been convicted of crimes.
Deputy Prime Minister Prawit Wongsuwon said the calendars would not be in violation of any laws if they were being distributed for non-political purposes.
"The investigation must determine whether this is related to any political parties," he said.
"The government has no policy for this yet," Gen Prawit said.
In Ubon Ratchathani, 50 military, police and administrative officers searched an air condition service shop yesterday in Warin Chamrap district. It reportedly stored at least some of the calendars to give to red-shirt supporters in the province.
The calendars are said to contain the two prime ministers' messages involving New Year blessings and the coming general election.
A total of 5,553 calendars were found at the shop, according to officers. The boxes in which they were stored bore the name of the recipient, identified as Rathawee Phuiprom, the 46-year-old owner of the shop.
The sender's name was given as "Pluem".
Sarawut Janthadee, Ms Rathawee's son, told officers his mother went to Bangkok for business and he was taking care of the shop for her.
He said the boxes had been sitting in the shop for days but he did not know who sent them.
Mr Sarawut was invited to give his account at Warin Chamrap police station. He has not been charged.
A source in the team that searched the shop said officers merely wanted to seize the calendars, and that no charges have been pressed.
The source said Ms Rathawee was a core member of the red shirts in Ubon Ratchathani. The calendars have been given out since October.