If you use Addon Spawner by IKT, https://www.gta5-mods.com/scripts/add-on-vehicle-spawner, you can drop this small picture in this location:

Grand Theft Auto V\AddonSpawner\img

This will put a thumbnail in the car spawner for you to see the car before you spawn it, a nice little touch! You can also make your own if you'd like to.