I once got caught up in a DUI checkpoint where they did the same thing. But the sign for it was right past the exit, but could be read before you passed the exit.

It happened to be my regular exit I needed to take to get home. There was a DUI checkpoint at the bottom of the exit ramp and it could not be seen from the highway.

I was coming home from my night job, and.... I do not drink alcohol. But one cop tried to use a bit of word trickery on me. After the normal questions he said in a seemingly forced casual way "Well, if you are drunk, you sure fooled me "... and then he obviously waited for me to say something. I did not say anything. He looked away, said something else (I do not remember what) and then looked at me and said the EXACT SAME LINE. "Well, if you are drunk, you sure fooled me". Again he paused waiting for me to respond.

At this point I knew something strange was going on, but not exactly what. So I asked if we were done, because I wanted to go home. He let me go.

Later on after thinking about it I realized if I had responded with anything like Yes, yeah, uh-huh or even vaguely moved my head as a nod .... it would be as if I had said yes I am drunk and fooled you. And then the cop would have me.

It was the first DUI checkpoint I had ever been in. Funny thing, about a year later my state government defunded dui checkpoints to basically stop them. Saying cops can do saturation patrols instead,

Sixty-six Missouri law enforcement agencies, including the Kansas City Police Department, lost funding for sobriety checkpoints in 2017 after the Missouri General Assembly passed a law shifting more than $19 million in federal funds away from checkpoints to saturation patrols. (Sep 19, 2023)