菇凉以后只许笑不许哭
[gū liáng yĭ hòu zhĭ xŭ xiào bù xŭ kū]
It's an affirmation for someone, likely oneself or a dear one. A 'Gulin' is a colloquial endearment for girls. In the second half, it demands only smiling but never crying in the future. That shows a positive and hopeful outlook, urging the girl(s) to remain happy no matter what.