Outside, female soldiers sat behind a plastic pot plant, smiles affixed, as they signed in new arrivals.
But inside, with doors closed and tea and biscuits served, Major General Sarayuth Rungsri, the regional army commander, wasted little time. Reading out orders from the new military ruler, General Prayuth Chan-ocha, Sarayuth had a blunt message for civilian officials: squelch anti-army dissent, or be transferred.
Such a call reflects the army's unease about whether it can ensure control of the country's north and northeast, both hotbeds of support for the deposed government of Prime Minister Yingluck Shinawatra.
Chiang Mai, home of the Shinawatra clan, is a particular challenge. Protests, banned since Thursday's coup, have swelled in recent days in line with growing opposition on the streets of Bangkok.
On Saturday evening, a crowd of about 200 people faced off with the army near the walls of the old city, lighting candles and jeering at armed soldiers. Phalanxes of troops periodically plunged into the crowd to grab vocal protesters, leading to sporadic scuffles and the detention of at least six people, Reuters reporters saw.
Missing from the scene have been the organised protesters by the "red shirt" supporters of the Shinawatra family, in particular Thaksin Shinawatra, Yingluck's brother, who was himself prime minister until he was deposed in Thailand's previous coup, in 2006.
Troops have shut down the city's pro-Thaksin radio stations and have held 16 local leaders of the movement incommunicado, one fugitive red shirt leader, who declined to be identified, told Reuters.
"I don't think we can do much at the moment since they've taken our radio equipment away. We'll have to put our movement on hold for a couple of months since the army is closely watching us," he said.
Army commander Sarayuth told Reuters only three red leaders had been detained. "We're taking good care of them, regardless of their colours," he said.
"AGAINST THE COUP"
Thaksin's loyalists had previously warned that a coup would be met with bloodshed.
A leader of one group, Rak Chiang Mai 51, Worawut Ruganapinunt, told Reuters on May 8 that a military takeover would lead activists to declare autonomy for the north's 17 provinces.
"We will close down the north by occupying provincial halls and blocking key roads," he said.
That hasn't happened. Instead, as of Saturday night, Worawut was among those confirmed detained by the army.
Red shirts have also warned that a coup could trigger mass defections among the strongly pro-Thaksin police and some soldiers. Only a handful of police could be seen at protests in Chiang Mai since the coup.
Two mid-ranking police officers interviewed separately by Reuters, who declined to be identified, said local officers would at the very least be half-hearted in aiding a military crackdown against coup dissenters.
"Ninety-seven percent of police are against the coup," one police lieutenant said.
"We will perform our duties for now, but if worst comes to worst and we are given orders to disperse crowds then we will give power back to the people."
Thaksin was a policeman before going into the telecommunications business.
The officer said many police could switch allegiance to a pro-Thaksin government in exile, if one was set up.
"In the end, you have to choose clearly which side you are on," he said.