A graphical mark specifically used to identify a company, organization, product, or brand is known as a Logo.
Why Logo is Correct
Logo: This term precisely matches the definition given – a visual symbol used for recognition.
Why Other Options Are Incorrect
Design: This is a broad term referring to the planning and creation process, not the specific identifying mark itself.
Pictogram: While a logo can sometimes resemble a pictogram (a symbol representing a concept or object), a pictogram is a general category, and not all pictograms function as brand identifiers.
Illustration: This refers to a visual artwork, like a drawing or picture, used for explanation or decoration, not typically as a primary brand identifier.
Therefore, the most accurate term for a graphical mark used for identification is a Logo.