Can cops drive with their lights off at night and still pull u over?

I was coming home from the store. It was 730pm. Dark out. I was doing the speed limit, driving in the left lane. I checked my mirrors and put my turn signal on and slowly moved over. A second later i had a cop with his red n blues behind me pulling me over. He proceeded to tell me i cut him off and he gave me a ticket for improper signal. Sure as day, he had his lights off and he was in my blindspot apparently. Can he give me a ticket?