As the white paper was torn away from the yellow wall, a wave of applause passed through the crowd.
Beneath it, four words were sprayed in Hungarian in red paint: "Eljen Laszlo Tokes - Szabadsag" ("Long Live Laszlo Tokes - Freedom!").
For this 20th anniversary of the start of the revolution in the western Romanian city of Timisoara, the Reformed Church chose to restore the original graffiti to its place under the window.
This was the window from which Pastor Laszlo Tokes, an ethnic Hungarian vicar, spoke to the crowds who came to try to prevent his arrest by the Securitate - the secret police - on 16 December 1989.
The crowd swelled, and marched on Communist Party headquarters. It then returned to the streets the next day, and the security forces opened fire.
As news of the massacre spread, people took to the streets in other cities, in solidarity with Timisoara. By 21 December, the waves which began in this city had built up into the tidal wave of Bucharest.
And on 22 December the dictator, Nicolae Ceausescu, fled. He was caught, tried, and executed by a firing squad on 25 December.
20 years on, the BBC has gained access to a remarkable document, the Timisoara station-master's log from November and December 1989. Hand-written, it meticulously records the details of each train which arrived in Timisoara North railway station during the revolution.
Placed alongside the military log-books of the army, the testimony of eye-witness, and those pages of the secret police archives which were not destroyed, the railway notes will help historians get closer to the truth about the revolution.
They may also help prosecutors - if any of the 440 people identified so far by investigators as participants in efforts to suppress the revolution are ever brought to trial.
The log-book was hidden until this year, and was provided by an anonymous person.
"You never met me," he told my colleague, as he handed it over at a late-night meeting. "We never had this conversation."
On 16 December 1989, between 2040 and 2240 in the evening, single wagon train 15/II arrived in Timisoara from Bucharest. It was met by the station chief.
All other trains had to make way for it.
The timing is significant.
The protest gathering was still outside Pastor Tokes's house - the marchers had not yet moved off into the city. According to Radu Tinu - at that time the number two in the Timis county Securitate - the deputy police chief of Romania, the deputy chief prosecutor, and a Securitate general were on that train.
"I had a horrible week, with hardly any sleep," he told me. He watched the revolution unfold before his eyes, collecting information based on phone taps, bugged buildings and a wide network of informers; and then details of the casualties. He made daily reports to his superiors in Bucharest.
Uniformed security forces first opened fire on the crowd on the afternoon of 17 December.
To this day, former Securitate officers like Mr Tinu blame the army, and the army blames the secret police for the killings.
"We were just an intelligence service. So what we had to do was to get our information and to analyse it.
"Whatever happened down in the street was the problem of the police and the gendarmerie."
More than 1,000 people died during the revolution, including 72 in Timisoara. In one of the most gruesome episodes, 48 bodies were taken from Timisoara hospital and driven to Bucharest.
There, their bodies were incinerated, and their ashes scattered in the snow.
The station master's log book provides evidence of other efforts by the authorities to crush the revolt.
It tells how the electric power supply was cut "accidentally" between Timisoara North and Timisoara East stations.
It shows details of unscheduled trains arriving in the city from other parts of Romania, loaded with workers' militia, armed with wooden bats distributed at army barracks, to punish the people for their disloyalty.
One of the first successes of the crowds was to persuade those workers to join the revolt. After that, the army in Timisoara came over to the side of people too.
'Troops to disembark'
There is another intriguing entry, from 0755 on the morning of 21 December. The protests had spread to other cities by then, but Ceausescu was still in power in the capital.
Supplementary train 1006/A, with two brand new carriages, their windows blacked out, loaded with USLA - anti-terrorist troops - arrived in the outskirts of Timisoara.
"Comrade Captain Brustureanu will indicate where to stop, at the Aradului Boulevard bridge, where the troops will disembark," reads the entry.
From there, they set out across the botanical gardens towards the city centre. Were they sent to fight the army, and seize back control?
One of the tragedies of the Romanian revolution was that so many people died actually after the dictatorship fell, in battles between the army and unidentified "terrorists."
Many were civilians, hit by stray bullets. The youngest victim in Timisoara was just two years old. Few people have ever been put on trial, and fewer still convicted.
Walking down the street, late in the evening, past the ground-floor flat where Laszlo Tokes used to live, we see two small children standing at the window from where he once addressed the crowds, gazing in wonder at the falling snow.
Instinctively, I raise a hand, in greeting.
They hesitate, then wave back.