Define symbol characteristics. Each SYMBOL statement specifies a color, symbol type, and size for the plot symbols, and connects the data points with a straight line. SYMBOL2 specifies a solid triangle as the plot symbol by combining FONT=MARKER with VALUE=C. 
symbol1 color=red
        interpol=join
        value=dot
        height=3;
symbol2 font=marker value=C
        color=blue
        interpol=join
        height=2;