<p>Four iterations of a "box fractal" or "Vicsek fractal", derived by iteratively replacing a square with a saltire or cross of five smaller squares on a 3-by-3 subgrid.
</p><p>Top:  Four iterations of the saltire form of the fractal.
</p>
Bottom: Four iterations of the cross form of the fractal.  The second iteration is a form of the "cross crosslet" symbol of traditional heraldry.
AnonMoos
<p>Self-made graphic, converted from the following vector PostScript source code:
</p>
<pre>%!
.5 dup scale/sq{3 mul exch 3 mul exch moveto 3 0 rlineto 0 3 rlineto -3 0
rlineto closepath fill}def/X{0 1 sq 1 1 sq 2 1 sq 1 0 sq 1 2 sq}def/T{0 0 sq
1 1 sq 2 2 sq 0 2 sq 2 0 sq}def/x{0 1 X1 1 1 X1 2 1 X1 1 0 X1 1 2 X1}def/t{0 0
T1 1 1 T1 2 2 T1 0 2 T1 2 0 T1}def/X1{9 mul exch 9 mul exch gsave translate X
grestore}def/T1{9 mul exch 9 mul exch gsave translate T grestore}def/X2{27 mul
exch 27 mul exch gsave translate x grestore}def/T2{27 mul exch 27 mul exch
gsave translate t grestore}def/xx{0 1 X2 1 1 X2 2 1 X2 1 0 X2 1 2 X2}def/tt{0
0 T2 1 1 T2 2 2 T2 0 2 T2 2 0 T2}def/X3{81 mul exch 81 mul exch gsave
translate xx grestore}def/T3{81 mul exch 81 mul exch gsave translate tt
grestore}def/sqq{/s exch def 1 .7 .8 setrgbcolor 0 0 moveto s 0 rlineto 0 s
rlineto s neg 0 rlineto closepath fill 0 setgray}def
gsave 10 10 translate 27 dup scale 9 sqq X 0 11 translate 9 sqq T grestore
gsave 307 10 translate 9 dup scale 27 sqq x 0 33 translate 27 sqq t grestore
gsave 604 10 translate 3 dup scale 81 sqq xx 0 99 translate 81 sqq tt grestore
gsave 901 10 translate 243 sqq 0 1 X3 1 1 X3 2 1 X3 1 0 X3 1 2 X3 0 297
translate 243 sqq 0 0 T3 1 1 T3 2 2 T3 0 2 T3 2 0 T3 grestore showpage
%EOF</pre>