There’s a total of 85 billboards
to smash. They are available right at the start of the game and appear on the map whenever you drive close by one. To find out how many you have collected, you can either check the district summaries on the map or the collectibles stats in the menu.
I have created an interactive map
that includes all billboards (and other points of interest):https://swissgameguides.com/maps/need_for_speed_heat/palm_ci...
All billboards are pretty easy to collect as most will require a speed of ~60-80 mph. Some of them require a minimum speed of up to 130 mph to be reached, but those billboards/ramps give enough space for long run-ups to build up speed. Other boards are also easier to get with off-road cars as the run-ups are mostly on dirt ground.
I’ve used the default Land Rover “Range Rover Sport SVR ‘15” which costs $107’000 and has good off-road qualities that are helpful when traversing the map in general.
The two billboards in Downtown Palm City that can only be accessed via the monorail can also be collected during the Time Trial “Trail Rail” (in case you fall down, it will respawn you on the rail).
If you want to get all collectibles at once, you should wait until REP level 13 in order to unlock all types of collectibles incl. billboards, street arts and flamingos.FYI:
I’ve taken screenshots for all collectibles that will be added to the map soon.