What is hidden in 3D image?

Driving to work, a gentlman had to swerve to avoid a box that fell out of a truck in front of him. Seconds later, a policeman pulled him over for reckless driving. Fortunately, another officer had seen the carton in the road. The policmen stopped traffic and recovered the box. It was found to contain large upholstery tacks.
"I'm sorry sir," the first trooper told the driver, "but I am still going to have to write you a ticket."
Amazed, the driver asked for what.
The trooper replied, "Tacks evasion."