Send an anonymous letter by mail or even better send it certified.
and put the return address as "the neighbor hood watch" n main st.
that will freeek him out.
That's the route I'd take.
Perhaps these idiots are truly not aware of the signature they are creating in front of their own damn home, and the repercussions of creating such a signature.
I'd send them an anon letter clearly outlining:
1. The traffic signature they have ALREADY created which is commonly associated with illegal drug activity.
2. The fact that if I noticed this activity, OTHERS in the hood are likely to have noticed the same damn thing.
3. The fact that my intent is NOT to have them locked up, but rather to highly recommend they move their business to a more secure location out of the hood, as their activity WILL eventually be met with complaints.
4. The fact that OTHERS who have noticed probably WANT them locked the fook up, and have or WILL notify LEO's.
5. The fact that since their signature has been so large, they are probably already under investigation by LEO's.
6. The fact that the safest course of action is to assume the operation is ALREADY compromised, and it is best to immediately stop operations from the residence, and to clear the residence of any unlawful materials that will be used against them should a warrant be issued to search the residence.
IMO, this approach has a far greater chance of being effective than any "tough guy" approach, and it doesn't implicate you in the process, so they can't point to you for retribution.
Do what you think is best, and good luck.