Find this already shot up police vehicle right outside of the starting zone. In the picture you should see a sign that says join the fight and once you are next to the shot up police car crouch where I am crouching in this picture and press your left and right mouse buttons simultaneously. This will bring up a prompt to enter the car. Once inside grab the treasure map.

At this point I really don't have to leave many tips, the treasure map will ping the location of the lost treasure on your map. Once you find the treasure you will get a bounty of weapons, ammo, and armor! Have fun!