gmt begin map_degree_symbol
    gmt set FONT_TITLE 18p MAP_TITLE_OFFSET 0p
    gmt subplot begin 2x2 -Fs5c/2c -M1c
        for symbol in ring degree colon none; do
            gmt basemap -R0/2/0/1 -JM5c -Baf -BWSen+t"$symbol" --MAP_DEGREE_SYMBOL=$symbol -c
        done
    gmt subplot end
gmt end show