Is placing the phrase "There is no god but Allah, Muhammad is the Messenger of Allah" on a car with the intention of ongoing charity permissible?

Placing a paper with "لا إله إلا الله محمد رسول الله" (There is no god but Allah, Muhammad is the Messenger of Allah) written on it in a car falls into two categories:

1. Permissible and Recommended: If it is in a respectful place inside the car, and the passenger benefits from it as a reminder of Allah or a supplication. This is not considered an ongoing charity (sadaqah jariyah), but the doer may be rewarded for it if their intention is to remind others. 2. Not Permissible: If it is outside the car or in an undignified place inside it, because that entails disrespecting the name of Allah the Almighty and the name of His Prophet, peace and blessings be upon him.