Miss Pross's statement that "hundreds of people" traverse the streets before the Mannette house is an example of the figure of speech of hyperbole while, along with it, the literary technique of foreshadowing is employed, incorporated in the same phrase.
That Miss Pross's statement is an obvious exaggeration used to create emphasis or effect is evident from reading the first paragraphs of Chapter 6 "Book the Second" of A Tale of Two Cities:
The quiet lodging of Doctor Manette were in a quiet street-corner not far from Soho-square.... Mr. Jarvis Lorry walked along the sunny streets from Clerken well where he lived, on his way to dine with the Doctor. After several relapses into business-absorption, Mr. Lorry had become the Doctor's friend, and the quiet street-corner was the sunny part of his life....
A quainter corner than the corner where the Doctor lived, was not to be found in London. There was no way through it, and the front windows of the Doctor's lodgings commanded a pleasant little vista of street that had a congenial air of retirement on it....It was a cool spot, staid but cheerful, a wonderful place for echoes, and a very harbour from the raging streets.
The reason that Miss Pross exaggerates so is the fact that the devoted Englishwoman is upset about her "Ladybird" who has "dozens of people" come who are not worthy of her and "come looking for her." When Mr. Lorry asks her, "Do dozens come for that purpose?" Miss Pross replies, "Hundreds." At this point, Dickens adds a note of direct characterization:
It was characteristic of this lady (as of some other people before her time and since) that whenever her original proposition was questioned, she exaggerated it.
Mr. Lorry realizes that Miss Pross is "very jealous," but she is also one of those women who become devoted to the person for whom they work. Miss Pross, therefore, exaggerates because of the "faithful service of her heart," the resentment for the attention of Lucie being taken from her, as well as considering the suitors, Darnay and Carton as both unworthy of Lucie.
Miss Pross' comment about "hundreds of people," in Charles Dickens' novel, A Tale of Two Cities, literally refers to the sounds of footsteps passing by their home, and the noise from the foot traffic that, through some strange acoustical phenomenon, sounds as if the Manette house is receiving hundreds of visitors.
In Chapter Six: "Hundreds of People", of the Second Book: "The Golden Thread," Mr. Lorry visits the family and he, the Manettes, Miss Pross, Darnay and Carton enjoy a pleasant evening. However, Miss Pross' comment about the hundreds of people continues to puzzle Mr. Lorry. Literally, it sounds like many people are rushing to see them.
In terms of the figure of speech it represents, it is exaggeration and called hyperbole. The phrase has two functions, and, as used, it is also the literary device technique of foreshadowing. So Miss Pross' tendency for exaggeration--hyperbole--foreshadows upcoming events.
Dr. L. Kip Wheeler describes foreshadowing as:
Suggesting, hinting, indicating, or showing what will occur later in a narrative. Foreshadowing often provides hints about what will happen next…Often this foreshadowing takes the form of a noteworthy coincidence or appears in a verbal echo of dialogue.
Foreshadowing is something that is often not noticeable until the event it hints at has passed and one can look back to see that a clue had been left regarding this event. In this case, at the time this chapter is unfolding, thoughts of the recent trial are fading, and this particular evening is a welcome interlude; even Mr. Lorry is thankful to have found himself a part of this family.
eNotes.com's analysis of this chapter reveals:
There is a sense of normality and quietness to this chapter, but hints are given that this quiet normalcy is about to be shattered.
Other examples of impending "disaster" are seen in Dr. Manette's inability to put his memories of his time in prison aside; his strange look at Darnay which is reflective of the secret knowledge Manette harbors about the younger man; and, the rushing sounds of footsteps that build to a crescendo in the midst of a fierce storm of thunder and lightning will point to the future developments of the French Revolution, and how they will be played out and affect the Manette family and their circle of close friends.
The echoing footsteps are an obvious foreshadowing that something involving crowds of people is about to happen. And the coming storm can be seen as yet another symbol of trouble to come. The final paragraph of this chapter further shows that something ominous is bearing down on the people in Dr. Manette’s house.