空飛ぶ鳥に迹なし Sora tobu tori ni ato nasi.　From Dhammapada in Pāli / Sanskrit; 法句經 pinyin Chinese: fǎjù jīng; Hokkugyou in Japanese, 真理のことば (Sinri no kotoba), a well-known title translation in Japanese
Flying birds leave no traces in the sky.
Connotation can be: In any case, we should do the right thing, even if people are not watching.