It appears at random on the quiet streets of Coupeville, sitting by Main one day, maybe Broadway the next. It watches you, cyclops like, as you motor past, its face a lighted mirror that registers your proximate adherence to the laws of the road.

If the digital numbers on that face read above 25 mph, it’s not smiling. Good advice: You might want to put the lead in, and slow down some.

Since early this year, the Coupeville Town Marshal’s office has been placing its new speed reader board at key locations around town as a reminder of posted speed limits. The machine was purchased through a $2,400 grant from the state Traffic Safety Commission, and been put to good use; this year, traffic violations have been cut in half.

“It has really made a difference,” Marshal Lenny Marlborough said Wednesday. “Rarely do cars go one or two miles over the speed limit,” when the board is in sight.

The reader board, which is hooked to a one-directional radar gun similar to those used by the State Patrol, was meant to be plugged into a cigarette lighter and mounted on a trunk, but Marlborough modified the thing for the particular needs of a smaller jurisdiction. The marshall penciled out a design that ties the machine, called a K-Ban radar system, to a 12 volt battery and some wheels.

The idea, he said, was to make the radar “self-sufficient,” just like another member of the force — Officer R2D2, if you will.

“I simply went to a tool company and purchased a trailer, bought some supplies,” Marlborough said, adding that his biggest concern in building a housing for the board was visibility. “I wanted that reader board up high enough to where it was easily readable by the driver,” he said.

The design, which Marlborough said he modified from other departments who have created similar set-ups, was a cinch. Kids at Coupeville High School’s shop put it all together. The whole shebang cost less than $400.

Marlborough said the idea for the roaming reader board originated in the realization that Coupeville cops were making a high percentage of traffic citations, and it wasn’t townies they were stopping.

“Looking at who the violators are, they’re people from out of town,” Marlborough said. “When you have an effective traffic program, locals are aware of it.”

He added, “Our problem was our education effort was being felt by our local population, but traffic was still coming in.”

Marlborough needed a way to catch the attention of tourists and passers-through. “Our local law enforcement action was not doing any good, so what we had to do was find a way to get the attention of the people that were visiting,” he said, adding with a chuckle: “And I think we’ve done that.”

Where the board gets set up any particular day is typically random. “We bounce it all over the place,” Marlborough said. However, he has received requests for the radar from concerned residents who want folks to slow down in their particular neighborhood.

Usually, the machine is plunked in high-volume areas such as Main Street, especially near school zones. And it never takes a day off (at least not until it decides to join the union).

Apparently, it works wonders. “The number of violations on Main Street this summer has been a fraction of what they were last year,” Marlborough said. “Even the students have noticed.”

And what about racers tempted to use the radar to test their own drag-strip skills, just to see how fast they can go? Marlborough said he has yet to see anybody misuse the reader board, perhaps for good reason. “I can tell you that if you see that reader board around, chances are there’s an officer around watching it,” he said.

In fact, Marlborough said watching the effect of the machine on traffic is amazing, with drivers tapping their brakes to keep their average speed decisively under the posted limit. “We get a kick out of sitting there and watching it,” he said, adding that he’s seen bicyclist who have hit close to 25 on the readout. (Marlborough said he has yet to test his fastball on it.)

The radar is unlike the speed guns used by staties, in that it one registers the speed of cars approaching it. The distance at which the radar picks up an approaching vehicle depends on the board’s position and the size of the car, though Marlborough said the machine picks up most cars within a block.

“It’ll have you on the radar before you are able to read it,” he said.

Marlborough, who calls the radar a “good investment,” said the board has been so successful the Island County Sheriff’s Department has asked to borrow both the machine and copies of the plans to build it. And it’s not only cops who like the reader board.

“It’s been met with a lot of positive comments, and not one negative,” Marlborough said. “The community has seemed to embrace it.”