白绢黑字君莫忘
[bái juàn hēi zì jūn mò wàng]
This phrase can be interpreted as 'white silk with black ink: do not forget it'. Here white silk refers to letters or messages in ancient times. So the overall meaning implies sending heartfelt reminders or promises in black words on white paper to beloved people so that they won't be forgotten. Meanwhile, there's also an atmosphere of history or classical romance behind it.