The Armée du Nord was set in motion on June 5, 6, and 7.  Napoleon’s Maison organized for campaign.

Hobhouse’s diary entry for June 7 included, “The Imperial Guard has nearly all marched – only the depots remain – the Nation Guard do duty at the Tuileries.”  (from Peter Chonchran’s, Houbhouse’s Diary, 17 – Hundred Days, page 235)

These events would not go unnoticed.

And they didn’t.

Lettow-Vorbeck included an intelligent timeline in the 1906 edition of his Napleons untergang 1815, on page 514:

Comte de la Porterie (Mons). A man he sent to Paris had learned from an adjutant of General Bertrand: Napoleon leaves the 6th, is in Douai the 7th, will make a false attack on Charleroi from the 7th – 10th, then throw himself on Mons and Tournay, The headquarters are in Laon.

Jean-Charles-Louis Regnault, in his famous La Campagne de 1815 – mobilisation et concentration, 1935, pp. 221-221, commented on the potential of Bertrand betraying Napoleon:

It was natural that the Emperor should be betrayed by Fouché, but that he was surrounded to such a degree by traitors is more surprising and it is especially difficult to accept the betrayal of the wife of the Grand Marshall of the Palace, one of the Emperor’s most devoted companions.
But when one sees Wellington disregard the precise information gathered by his outposts, and believe only that coming from Paris and from the imperial entourage, ultimately to be surprised by the opening of hostilities, one must recognize that the only result, achieved through betrayals, was to put him in a fairly perilous position.
Was the Emperor truly betrayed or, on the contrary, did he not play with the mirage of betrayal, so frequent during this period, in order to fool his adversaries?

In Wellington’s Despatches Volume 10, starting on page 442, we find:

The Prince of Orange to Field Marshal the Duke of Wellington.

Braine-le-Comte, 6th June, 1815.

My Dear Duke,
I send March with the two enclosures from General Dornberg and General Behr, which I thought you might wish to have without loss of time. I received, besides, this morning a report from General Collaert, in which he says that he knew of General Albert, who commands the French cavalry, having said that if we did not attack on the 7th, they would attack us on the 8th or 9th. If nothing happens tomorrow, I hope to see you at your ball.
Ever most truly yours,
William, Prince of Orange.

first enclosure

I have the honor to report to your Royal Highness that Mr. Vilnoisy, sent to France by His Majesty Louis XVIII 12 days ago, left Paris on Saturday, this June 3, after having seen the celebration of the Champ de Mai, that he reports to have been utterly combative, actually absolutely warlike, soldiers having rolled out all of the embellishments possible: he says, too, that the outskirts of Paris are fortified such than entry is impossible without being stopped, held by an assembly of Forestry guards, [farmers], gendarmes, etc., with a very exact surveillance.

He is announcing the departure of the Emperor for this day, 6 June, going to do the inspection of the French cavalry in Douai, commanded by General Milhaud: this inspection must
take place on the 7th. From there he will go to Compiègne, on which road are directed many troops coming from Paris: thus did he see in every city, on the roads and ways of this last city on the border, cars in great number to transport the troops by coach; observing that in the small city of Moye two hundred cars were assembled destined for this purpose, and that a rumor was circulating that the national guard was to make use of them, but that people better informed assure are for the line troops who are headed toward Laon, Compiègne, and Douai: he similarly assures to have liaised with employees working on the movements of the military operations in Paris who have assured him that the Emperor would transport himself personally to Avesnes, in order to have a false attack on the Allies occur from the side of Flandres, between Lille, Tournay, and toward Mons: the same person saw an artillery park near Valenciennes with 80 pieces of canon, all of 8, which is established on the glacis (banks) of this city.

second enclosure

Major-Gen. Sir W. Dornberg to Lord FitzRoy Somerset.
Mons, 6th June, 1815.
My Lord,
The man of whom Count la Porterie speaks in the enclosed letter gives the following intelligence.
Buonaparte will leave Paris on the 6th, and goes to Douai, where he is to inspect the cavalry of General Milhaud. He will certainly attack as soon as possible; and he has said himself
he would have destroyed the Allies before the Russian army could arrive. It is supposed he would make a false attack on the Prussians, and a real one on the English army.
Four battalions of the Young Guard, under General Barrois, were still at Compiègne; four battalions of the same that were at Louvres, near Paris, have been marched to the Vendee, as
well as the reserve army that was in the neighbourhood of Paris. A considerable park of artillery (about 150 pieces of 8 and 4) left Vincennes six or seven days ago, and were directed
towards Laon. At Valenciennes this gentleman saw still the park of artillery, about 80 pieces, and a great number of troops in the villages.
I have the honour to be, my Lord, your most obedient humble servant,
Dornberg.

The reports of a feint on Charleroi and advance favoring Mons were received by both Allied armies.  But as Wellington explained, he “… preferred being late in m movement to having to alter it.”  The Allies received reports of Napoleon’s presence on the frontier or imminent attack during May and June, but did not react.  The French army was frantically organizing, and there were constant troop movements.  Maybe Napoleon contributed to rumors, maybe he didn’t, but it appears no special effort was necessary.  As Hobhouse observed, so did others.