Mark pattern on cake.
Bottom Scallops: Prepare cake marker with two pins, placed at the 1½ in. and 2½ in. positions. Using additional cake circles, raise cake so bottom pin is ½ in. from bottom of cake. Press pins into icing. Move marker 1¼ in. to right; mark again. Repeat around entire cake. Remove one pin. Position remaining pin at 2 in.; make marks between previous markings. Repeat around entire cake.
Middle Lines: Remove additional cake boards; place cake on level surface. Prepare cake marker with three pins, placed at the 1¾ in., 2½ in. and 3¼ in. positions. Mark lines in icing, moving marker horizontally and turning cake as needed. Remove one pin. Position remaining pins to 4 in. and 4¾ in. positions. Repeat; marking lines in icing.
Top Scallops: For top scallops, place pins at 4¾ in. and 5¾ in. positions. Repeat same process at bottom, lining marker up vertically with bottom markings. Remove one pin. Position remaining pin at 5¼ in.; continue making marks between previous markings. Repeat around entire cake.