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But the trip, say analysts, is emblematic of a key tactic from the Trump administration: cutting off North Korean revenue, no matter how small or obscure the source.
But there may have been an ulterior motive in choosing the destination -- Singapore-based businesses have been accused in recent years of helping North Korea evade sanctions.
Arms trade
Though no longer fully in power, the Myanmar military still wields a significant degree of influence -- and has come under scrutiny for its relationship with North Korea in recent years.
"At a minimum, he's going there to remind them that we (the United States) are watching," said Anthony Ruggiero, a former deputy director of the US Treasury Department and an expert in the use of targeted financial measures, during a panel sponsored by the Foundation for Defense of Democracies last week.
CNN has reached out to the Myanmar Ministry of Foreign Affairs regarding the trip and Myanmar's relationship with North Korea, but they have not responded.
"Global action is required to stop a global threat," Tillerson said. "Any country that hosts North Korean guest workers, provides any economic or military benefits, or fails to fully implement UN Security Council resolutions is aiding and abetting a dangerous regime."
"We will cut the money off to North Korea until they behave properly," said US Treasury Secretary Steven Mnuchin.
China's Foreign Ministry denounced the move, with spokesman Lu Kang saying Beijing was "against other countries imposing long-arm jurisdiction over Chinese entities or individuals based on their domestic law."
Guns and missiles
Firms in both Singapore and Myanmar have been accused of buying or selling weapons from North Korea.
He reiterated that to an email to CNN, saying Pan Systems Singapore had no connection to Pan Systems Pyongyang.
Myanmar was for years accused of purchasing Pyongyang's ballistic missile technology. Before free elections led to the rise of Aung San Suu Kyi, Myanmar's leader, the country's military was considered among the key allies of North Korea.
"Of course, Burma (Myanmar's previous name) was different back then," Ruggiero told CNN.
"The question I would have (now), is how many people in the Burmese military are still sort of around and interested in having that relationship with North Korea. And I don't know how much control she (Myanmar leader Aung San Suu Kyi) has over all of the government ... it only takes a couple of military officials who want to continue that relationship for it to continue."
Though plenty of sanctions have been lifted on Myanmar since the country's reforms, those with respect to North Korea have stayed in place, according to Ruggiero.
He's made no public statements regarding the accusation.
Options
The problem is global, with countries as far away as Africa being accused of violating UN sanctions against North Korea this year.
Senior administration officials say Sudan is making progress, but needed more time to review the issue.
The UN's 2017 Report from the Panel of Experts on North Korea accused Pyongyang of supplying guided rockets and missiles to Sudan in 2013.
The Sudanese government responded to the recent decision by freezing talks with the United States on the sanctions issue until October, according to the state-run Sudan News Agency.
With Yun's Singapore trip, the United States is likely trying to telegraph to North Korea that it will step up its own operations in places like Southeast Asia, where North Korean illicit activity has been tracked in past years, according to Ruggiero.
"The message to North Korea should be, if you're here, we're here, and we're going to give these countries and these banks and companies a choice -- continue to do business in the US dollar or work with North Korea," he said.
Pyongyang has been a part of the Northeast Asia Cooperation Dialogue that Yun is attending, though the State Department spokeswoman Heather Nauert said she was told North Korea is not participating this year.
Though the strategy could potentially starve North Korea of some of its money, it's unlikely to really tighten the noose on North Korea without the buy in of China, Kim Jong Un's most important benefactor.
Beijing accounts for about 85% of Pyongyang's imports, according to UN data, providing a key lifeline for the North Korean economy.
"Certainly billions of dollars are coming from China, but there's nothing wrong with concentrating on millions when it comes to Southeast Asia," Ruggiero said.