In a saucepan, melt margarine over low heat. Add marshmallows and stir until completely melted. Cook over low heat three minutes longer, stirring constantly. Remove from heat. Add crispy rice cereal. Stir until well coated. Press mixture into a 13" x 9" pan, coated with cooking spray. Remove from pan and place on foil-lined cutting board. Using red decorating icing, make straight line 9" across the center of mixture. On left side of line, make heart-shaped design using frosting. On the right side of line , write your own personalized message using red decorating icing. For a finishing touch, trim edges of greeting using frosting. Cut into two inch squares.