青青子吟悠悠我心
[qīng qīng zi yín yōu yōu wŏ xīn]
A line from 'The Book of Songs,' one of the earliest collections of Chinese poetry. Translating loosely as: 'The green collar you wear sings softly, lingering forevermore within my heart.', suggesting unceasing longing and affection towards a particular someone or something.