The druggies think that they get magical protection from the “saint”. That they are protected and some think they are made invisible to law enforcement. They mark the cabs of their rigs with charmes, amulets, etc. Makes it easier for them to be identified. US law enforcement is getting better at this. Stupid Mexicans.
I think this is what the movie Apocolypto was trying to point out. The meztizos are only a few steps out of the jungle. They are coming to a hometown near you.