OH yeah, we got those here too - dressed up in Mariachi whites & shaking maracas with signs on their front & backs. It's fun, but man it must be misery when it's hot out there!
After watching a local roofing contracter switch over almost entirely to illegal subs, I decided to start watching them in my neighborhood.
One day I noticed that a van they were using with Texas plates (here in Florida) had no registration sticker and was towing a trailer with FL tags.
The next day the van was gone from the house they were working on and three guys were now there in a white car - same Texas tag though was now on the white car.
You can never tell when you can get the ball rolling on a felony. Out of date temp tags, expired registration sticker, tags that don't match, etc.