Personally, I think it is the unique spin on things each person brings to their work, their life, etc. In many ways, the key to being unmistakable is to be yourself.
Of course, many people have trouble with that. I have trouble with that. There is that pull to imitate others, to mimic what has come before in an effort to assure success.
And I think this is where many people go awry with social media. They ignore and hide what makes them unique.
As Oscar Wilde advised, "Be yourself; everyone else is already taken."