This wonderful letterhead belonged to Roy Lichtenstein, a leading figure of the Pop Art movement known for his comic book-inspired paintings and use of Ben-Day dots. The illustration was taken from his lithograph Real Estate (1969). In an interview with Fine, August 1993, Lichtenstein joked, "If you write to enamel companies with that on your letterhead, they will take you seriously."
Source: Kindly sent to me many years ago by gallerist Dean Walker.