"Unmistakable appearance" means that something or someone has a unique or distinct look that is easily recognizable and cannot be confused with anything or anyone else. Full definition
«Appearances are everything,» said owner and lead stylist Perry El, a Queens native and entrepeneur that opened his first startup clothing line in 2012 to «provide exclusive men's fashion, custom suits and styles to the professional man with a unique and unmistakable appearance,» and as fashion evolved, so did his client base. (queens-politics.com)
The villain's unmistakable appearance can be seen in the background, relaxing in a chair on set. (cbr.com)
That lifeless body on the beach bears the unmistakable appearance of Harry Potter himself, Daniel Radcliffe. (film.avclub.com)