Why does he check his license plate often?

So there’s a drug house on my street. Super freaking annoying. They have all their clients park in front of my house. Well this one guy that’s been coming every single night that goes to that drug house (has a girl usually in the passenger seat, I’ve seen them both in a couple other vehicles before too) they always park directly in front of my house then go to the drug house. Every time the guy gets back to his car he checks the back of his car what looks like is his license plate. Why would he do that out of curiosity? He checks it every single time. I’ve also seen the drug dealer do the same thing to his multiple vehicles he has parked in front of my house as well. I have kids so I try to always be wary of our home surroundings. If we’d known this we wouldn’t had bought our home 2 years ago. Eventually we want to sell and move to a better more secluded area. It’s so uncomfortable knowing these random drug dealers and addicts are outside my house all hours of the day and night. There’s always space by the house they go to as well. Of course they want the traffic to look like it’s at my house smh. Cops have been anonymously tipped Mike times. Nothing gets done…I wouldn’t care if they didn’t do it in front of my house as if they lived here themselves smh.