Every typewriter is unique. Each model has it's own characteristics, including the typeface of course. Individual typewriters would also gain their own characteristics. A certain letter might become slightly out of alignment compared to the others, spacing might vary a tiny amount. Even the way someone typed was different. This allowed typewriters to be a focus for forensic examiners sometimes in criminal investigation as the typewriter of a suspect could be linked to a crime.
This is illustrated in the decent early 1940s crime drama The Panther's Claw. A man is suspected of being a blackmailer. One of the pieces of evidence the police seek out is an example of typing from the suspect's typewriter so they can compare it against the ransom note. Of course criminals also knew that typewriters could be used to identify them and link them to crimes, in the late 1930s film The League of Frightened Men a suspect manages to prevent a detective from getting a type sample from their machine.
So the moral of this is, if you are intending to commit a crime make sure you use someone else's typewriter!
