Complex sentence: The series title refers to the artist's practice of embellishing existing printed matter with his ballpoint "doodles", (a convenient alternative to the risky process of applying paint to walls) often adding ironic additions to what is already pictured within the advertisement.
Split into simpler sentences: The series title refers to the artist's practice of embellishing existing printed matter with his ballpoint "doodles," (as (opposed) to the risky process of applying paint to walls). Often adding ironic additions to what is already pictured within the advertisement.