Destroy all For Sale Signs
Meet with Josh outside the mansion in Rockford Hills, then simply go to the website Josh texts you with. Here you’ll want to go to the “Find Properties” map and it will open up a map of all the properties you need to visit. Click on each one and click “Get Directions” to have a waypoint marker added to your minimap.
All that’s left to do is visit each house and deface the sign outside. Shooting them, running them over, throwing explosives. Whichever sadistic method you want to use is fine.