One form of an architectural/symbolic "quatrefoil", made of four overlapping circles.  In the version of the quatrefoil shown, the circles are pulled almost as far apart as they can be and still have the circumferences of the innermost circular white areas intersect.  For different versions, see Image:Quatrefoil-Architectural.png and Image:Quatrefoil-Architectural-Square.png. 

The quatrefoil is the fourfold version of an architectural trefoil (see Image:Trefoil-Architectural.svg).
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
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%EOF
AnonMoos (PostScript and PNG source); Amada44 (first-uploaded SVG file)