[CherryMond]

You can try this: https://sampforum.blast.hk/showthread.php?tid=544162

Possibly create an object, add text on it and attach it to the vehicle?
https://sampwiki.blast.hk/wiki/CreateObject
https://sampwiki.blast.hk/wiki/SetObjectMaterialText
https://sampwiki.blast.hk/wiki/AttachObjectToVehicle