The painting is "I Love You with My Ford" (1961) by James Rosenquist (b. 1933), who is usually labeled a Pop Artist, even though he insists that the term is misleading and, in any case, does not apply to him.
I confess that my knowledge of the personal lives of modernist artists active after the 1930s is rather thin, because I don't like most of their work. So I was surprised to learn (even though the rest of the world knew it) that Rosenquist gained much of his early experience as a painter doing billboards in New York City. Which is why his paintings are large as well; he knew how to do it.
A biographical sketch on Wikipedia is here and a chronology on Rosenquist's own Web site is here. A few years ago, Rosenquist and a collaborator wrote this rather interesting autobiography. It contains a few observations about art I'd like to pass along.
Billboard painting was really like an old master's school of painting. These people were journeyman artists, in a tradition that went back to the painters' guilds of the Middle Ages. The nearest thing to it would be for a kid to be mixing colors in an ink manufacturing plant. You would get to know color pretty well doing that. Of course there are still the scenic artists who work on Broadway shows. That's quite a complicated business because they use water-based paints that dry darker and differently than when you are working with them wet. They have to use water paint so it won't catch on fire so easily. That would be the nearest thing to getting an education painting billboards. [page 49]
[His thinking circa 1960] I wanted to do something totally different from anything being done by everyone around me. All the artists I knew had been taught to use paint expressively, to splash paint on a big canvas, look at the big blob you'd created and to have it suggest something back to you. It seemed to me too simple to put a mark on the canvas and have that be it. Once you've put that mark on the canvas you have the responsibility of cleaning up the mess, of making something unexpected out of it because you started out with a white canvas that was beautiful to begin with.
My question was, what do you do with that mark? There's a difference between trying to achieve a predetermined idea and letting your random action dictate what it may or may not suggest. Now, I like the first first idea better for many, many reasons. If you tackle a huge canvas, unless your idea is planned out, as in mural painting, everything can, may--and usually does--go awry. [page 78]