Almost decked by impatient D-bag on left turn!

I was riding along Floyd Ave (25 mph zone) in Denver, Colorado USA at a healthy clip (25-28 mph), and intended to turn left at Columbine Circle. I signaled my intention to do so. In spite of this, the black Volkswagen (Colorado plate: QFZ-207) decided to recklessly pass me on the left at ~ 40 mph, into oncoming traffic. This reckless move bought him...nothing, since he ended up behind traffic at the next stop sign. When I quizzed him about his actions, he said, "I never saw your signal.