A quirky handmade sign discouraging littering...."Think before you throw your litter down, you may not care but I do".
Technically just encouraging the 'thinking' about it though, before explicitly describing the action that it is in fact discouraging (arguably 'shouting' in capitals') 'throw' your litter down'. That "throw" is a strong and active description, even angry, rather then a description of perhaps typically more nonchalant dis-guarding of litter.
The alternative is to encourage the desirable action. With the 'You may not care but I do - Please use a litter bin'. Or to reflect the request to think..."Please consider using a litter bin."
The original prose curiously opens up the question about whether the message had been left on behalf of the tree so giving it a voice, or possibly that the author is looking on.
