Authorities are hunting down those who spray-painted the letters "RKK" in Burmese and Arabic in red on roads in Surat Thani's Tha Chang district.
The find has puzzled them as the graffiti refers to the southern conflict but has appeared in a province not usually associated with the unrest.
RKK, full name Runda Kumpulan Kecil (literally, "small patrol groups" in Bahasa Malaysia), has operated for at least 14 years in the deep South.
The RKK group has the reputation as the most brutal of all the southern separatist gangs, and was believed responsible for most of the 54 beheadings in the deep South between 2004 and 2014. Its leader is Ismael "Ustaz Soh" Rayalong, who has led numerous bombing attacks in the region, particularly in Yala province.
Pol Lt Gen Thesa Sirivatho, the Provincial Police Region 8 commissioner who oversees the southern provinces, said he was alerted to the incident by Surat Thani police commander Pol Maj Gen Apichart Boonsriroj and asked officers to gather evidence at the scene.
Police and security officers in the South are investigating why the letters "RKK", which stand for Runda Kumpulan Kecil, one of the separatist groups responsible for attacks in the three Muslim dominated provinces of Pattani, Yala and Narathiwat, appeared in Surat Thani despite the fact it is far away from the three restive provinces.
Pol Maj Gen Apichart said when authorities arrived at the scene they found the messages written in red paint sprayed on three nearby roads in Huai Rien village in tambon Sawied of Tha Chang district.
Pol Maj Gen Apichart said he sent for an Arabic interpreter who said the message found at the first location on Asia 41 Road, 1km from Khuanra intersection, read "Welcome RKK fighters".
The second message was translated as "a place for selling speed pills" along with the letters "WY", a symbol for the illegal drugs found on a small deserted road in the village, he said.
About 500 metres away from the second location, the third message was translated as "Death route. Watch out."
Pol Maj Gen Apichart said officers had spoken to villagers who said they found the first message on Monday night.
The two other messages had remained on the road for a week.
Pol Lt Gen Thesa said he obtained information which suggested Myanmar migrants, who worked as rubber tappers and had knowledge of Arabic, could be responsible for the incident.
They might be protesting against the arrest of four Myanmar workers who were accused of stabbing an 18-year-old female student to death in Ranong last September. Police have asked locals to keep a look-out for suspicious activity.
Meanwhile, in Songkhla, a woman was killed and seven others wounded by two explosions that rocked a restaurant in Thepha district on Monday night.
According to police, a grenade was lobbed into the restaurant-cum-karaoke bar on Soi Sawan beach in tambon Ko Saba on Monday around 11.30pm.
The dead woman was identified as Wipawadee Roypuang, 28, from Na Chuak district of Maha Sarakham province.
Shortly after the first blast, another blast occurred in front of the same premises, about 10 metres from the first incident. However, nobody was hurt in the second explosion, police said. Police and military forces are investigating.