Extra Commission is a Strangers and Freaks mission for Trevor.

You meet Josh who wants you to go to every one of his rival's houses and destroy the for sale signs out front. Josh will soon send you a text with a link to the rivals website where he shows all of his houses. There are 15 signs in total.

Pick one and get the location for it and then destroy the sign. Have a system in order (left to right, bottom to top, etc.) to make this easier, and additionally mark each location where you destroyed a sign as a point of interest in order to prevent missing a sign.

After you have destroyed every sign, you will get another text from Josh telling you to meet him in a motel.