The ceilings were repainted. The gold trim was shinier. The floors were repaired. And there appear to have been renovations in the back, behind the grand columned entrance and marble staircase.
He believes these herald a moment in history: the reopening of a Cuban embassy in Washington, D.C., after a 54-year hiatus.
That suspicion is based on more than a mere hunch.
Mullaly runs a flagpole business. He started it a dozen years ago with a wheelbarrow, an old shovel and a pickup truck and has grown into several states and worked on various government buildings.
The Cubans got in touch with him early this year, after the surprise announcement that diplomatic ties were being restored with its old Cold War nemesis the United States.
The Cubans wanted bids for a pole at the property on 16th Street — the former Cuban embassy which was shuttered in the 1960s, then reopened as a de-facto Cuban interests office in 1977.
They told Mullaly that full-fledged embassies could soon return to Washington and Havana. Of course, embassies need flags and poles to fly them from. And thus began the most exciting project in the history of Eastern Shore Flagpoles, the business Mullaly runs with his wife.
After a meeting at the building, he was put on standby: "They said, 'If we give you the go-ahead we need this done within three days,'" Mullaly recalled in an interview.
He was called back a couple of weeks ago.
The U.S. government had dropped Cuba from a list of terrorism sponsors, a key demand for further detente. The big announcement is expected soon.
There was speculation the reopening might be announced last month but the lead American diplomat on the file, Roberta Jacobson, said there were still details to be worked out: "We've gotten closer each time we talk," she added.
A few days later, Mullaly got the go-ahead.
"They said, 'Okay, we'd like to install the pole'," he said.
"They sounded very excited. And I was excited to be a part of it. I think it's a wonderful thing. ... They were some of the nicest people I have worked with."
On a Monday earlier this month, he dug the foundation. On Tuesday, he did the brick work and installed a light at the base. And on Wednesday, with the help of a truck, Mullaly and two employees raised a flagpole outside the future Cuban embassy to the United States.
A few Cuban officials monitored the work. That crowd grew to about 30 or 40 people, with some people snapping photos.
"It was a proud moment," Mullaly said. "It was an honour to be part of it."
The actual flag — featuring blue and white stripes, a red triangle and a white star — will be hoisted whenever the embassy reopens — perhaps as early as next month.
The Obama administration says it plans to notify Congress first and give lawmakers the required 15-day notice. Some Republicans may try to stall the process, with talk of bills to deny funding for a Havana embassy.
If this whole process has created work for Mullaly, it's taking some away from Martin Dahinden.
He's the new Swiss ambassador to the U.S. Part of his job is to play a protective role for the Cubans working in the building on 16th Street.
Because the Cubans don't work in a recognized embassy, the Swiss occasionally help them with things like procuring diplomatic licence plates.
Dahinden was briefed on his Cuban responsibilities before he arrived for his new posting which officially began in mid-November. A few weeks later, he got a call informing him that the U.S. and Cuba were set to make a historic announcement.
He was delighted.
"It was good news," Dahinden said in an interview in his office.
The Swiss role itself wasn't especially complicated.
Certainly nothing like in the cloak-and-dagger days of the Cold War, when the Swiss acted as go-betweens during the Cuban Missile Crisis and after the Kennedy assassination.
Secretary of State John Kerry has thanked the Swiss for their help over the years, and everyone is now looking ahead.
"Our mandate will disappear," Dahinden said. "It won't be necessary any more."