The bottom of my home page has this as a PostScript signature:

    %!PS                           % -John Tromp http://tromp.github.io/
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    .8 mul .2 add setgray -1 1 scale t -1 2 translate t 1 -1 scale t[0 1
    1 0 0 2]concat t pop}{0 moveto 1 0 lineto 0 2 lineto closepath clip
    fill}ifelse grestore}def 10 10 translate 600 600 scale 5 t showpage