I feel comfortable making the sign of the cross anywhere. I think it should be done in the proper spirit however, with reverence, just as any prayer. My children make the SotC before meals at school. They aren't shy about it because they have not been taught to be. My kids are also starting to pray spontaneously, and I am so happy about it. My two year old has started taking his turn saying the prayer before meals at our house. The older children say the traditional, "Bless us, O Lord, and these Thy gifts, which we are about to receive from Thy Bounty. Through Christ our Lord, Amen." But Riley can only manage, "Peas Dod, Bess us. Amen." And he makes the SotC.

He is so precious. And we do this as a family before every meal, whether we are at a restaurant, or at the house of family/friends, or at our own home. I am glad that we have been an example for him, and the other children, to regard prayer as a natural occupation, and not something that we should feel self-conscious about. In fact, my children have told me that while visiting friends and eating with their families, they were made extremely uncomfortable when no prayer was said before eating. Being my children, they weren't too shy about going ahead with their own prayer before digging in.

But I imagine that glances were exchanged over the heads of the little ones.
The SotC comes very naturally to me now, though I felt a bit awkward with it at first. It is a beautiful blessing, and a humble reminder. Keep the Cross before you always.