Lay people should refrain from giving such blessings in Church because they are likely to be confused with the blessing only a priest can give. But it is appropriate to give a blessing to family members in private. Making the sign of the cross on the forehead is a good way of doing it because it is less likely to be taken as a priestly blessing.
When my grandmother kneaded the dough for bread, the last thing she would do was to make a cross on the dough with the side of her hand. The cross is the sign of our salvation. It is most appropriate for us to use it in our daily life.