Is this Standard Procedure or a Traffic Violation?

I was just wondering if it is standard procedure for a state trooper to flash their headlights on and off at you.

I was driving home last night at about 2:30 am.  I had just dropped a friend off that needed a ride home from an establishment.  I traveled from the area that I dropped him off at and headed up Main Street.  I turned on to East Main, and noticed headlights pulling out from behind the pet shop on East Main and Main.  I continued traveling, and by the time that I reached the Kwik Fill on East Main, the car was already about 20-30 feet behind me.

I looked down at my speedometer, figuring that I was going slower than the speed limit due to the amount of time that it took the car to catch up with me.  I was going 30 mph.  When I was in the area of Fisher Ave, the car behind me shut its lights off, and drove like that for about 5-6 seconds.  I looked in the mirror and it was a state police cruiser.  The state trooper turned his lights off, then on again, and I decided that he might be trying to get me to pull over for a reason other than a traffic violation.

I turned on my turn signal, and made a right hand turn onto Bagley Ave, the street right next to Togi’s Sub Station, and pulled in to the parking lot.  The cruiser continued down East Main.

By the time that I made it back on to East Main, the state trooper was out of sight.

Is this a normal tactic?  I thought that every vehicle was required to drive with headlights on when it is dark.  I didn’t know it was legal to drive any amount of time without headlights on.  Yet this trooper did it twice.  Was he hoping that I was drunk, and the light flashing would screw me up?

Please, if anyone has an explanation, please let me know.