Generated by means of the following PostScript code (change "56" to "57.1614716" to see the version of the quatrefoil where adjacent innermost circular white areas are exactly tangent, which results in a less aesthetic version of the symbol):

%!
306 396 translate
.8 dup scale
/x{56}def % 57.1614716
/a{c 0 360 arc fill}def
/b{-138 x sub 0 a 138 x
add 0 a 0 138 x add
a 0 -138 x sub a}def
/c{163}def b 1 setgray
/c{157}def b 0 setgray
/c{144}def b 1 setgray
/c{138}def b 0 0 a
showpage
%EOF