[Weirdosport]

Well you could choose either of these:

https://sampwiki.blast.hk/wiki/AttachTrailerToVehicle - Attached the trailer

https://sampwiki.blast.hk/wiki/IsTrailerAttachedToVehicle - Check if the player has a trailer or not.

For example, you could have trailer/roadtrain combinations and when the player types "/transport" it checks whether they have a trailer or not.