Their symbols were the rose, the myrtle, and dice. http://www.dl.ket.org/latin1/mythology/1deities/gods/lesser/group/graces.htm
A symbol for grace is a ballerina because it represents peace and tranquility.
If you are referring to the woven square knot that has 4 parts sometimes called a quadrequetta, this represents the 4 Gospels from the Bible and is found in "The Book of Kells" in many of it's...
The Celtic symbol of freedom and transcendance is the bird.