Seeing that the word “say” implies the spoken word, I would have to answer no. But I always “think” grace in public. Not from shame or embarassment or anything like that, but because I believe that it’s what I’m called to do by Matthew 6:5-6:
When you pray, do not be like the hypocrites, who love to stand and pray in the synagogues and on street corners so that others may see them. Amen, I say to you, they have received their reward. But when you pray, go to your inner room, close the door, and pray to your Father in secret. And your Father who sees in secret will repay you.
That verse speaks to me, and that’s why I don’t “say” grace in public. But that’s me; I don’t hold anything against those who do.