The two main conventions silent cinema used to suggest sound were images of sound-making objects and intertitles, which often used capital letters to make a word “sound” louder. The Artist masterly uses both to reinforce its narrative elements, the coming of sound and the main character’s inability to speak.
On the subject of speaking, the film constantly uses these devices to keep it present:
The film starts with the projection of a silent film starring the main character (in both films). In this particular scene he’s being tortured. What his tortures want is him to SPEAK, which he categorically refuses to do. Very clever trick, given that the film is about this actor’s refusal to speak for the “talkies”.
This sign further foreshadows the actor’s predicament.
This newspaper title reinforces the subject of speaking – “That’s the question on everyone’s lips?”
On the subject of the coming of sound, the film constantly includes microphones and headphones to suggest its presence:
Had this been a sound film, the microphone in the first clip might have been redundant. In the second clip, the presence of the equipment might have been a bit less prominent and the camera might have done without showing the interviewer putting his headphones on. In the third clip, the microphone sometimes even appears nearly at the centre of the shot, and there’s a reaction shot of the sound man (of all the people), who is in no way involved in the conflict of the scene.