How to say don't make a place ugly/untidy?
I have seen "Don't litter" boards in Railway stations; but can we use it in other places like, "Don't litter your room/car (keep it clean)"
Don't litter your room/car
sounds strange to me.
I have heard
- Don't clutter (up) your room/car.
- Don't dirty (up) your room/car.
- Don't keep/make a mess in your room/car.
However, instead of using "Don't", I would say
Keep your room/car clean.
This seems very natural to me.
To answer your question, yes you can say "dont litter your room/car" as that is correct. However, litter does not mean the same thing as ugly/untidy. You could have a beautiful litter or a tidy trash.