\startMPpage[instance=doublefun]

% Inspired by and largely copied from Donald Knuth's METAFONT dangerous bend glyph

h=11;

u=h/15;

w=h*8.5/4.6;

heavyline=2;

y1=25/27h;

x4=0;

x1+x1=x1a+x1b=x4b+x2a=x4+x2=x4a+x2b=x3b+x3a=x3+x3=w;

x4a=x4b=x4+u; x3b=x1a=x1-2u;

y4+y4=y4a+y4b=y3b+y1a=y3+y1=y3a+y1b=y2b+y2a=y2+y2=0;

y1a=y1b=y1-2/27h; y4b=y2a=y4+4/27h;

path signboard; signboard := z1a..z1..z1b---z2a..z2..z2b---

z3a..z3..z3b---z4a..z4..z4b---cycle; % signboard

fill signboard withcolor yellow;

x10=x11=x12=x13=(.5w-u); x14=x15=x16=x17=w-x10;

y10=y14=28/27h+epsilon; y13=-h*(6.6/4.1);

z11=(z10..z13) intersectionpoint (z1a{z1a-z4b}..z1{right});

y15=y11; y16=y12=-y11; y17=y20=y21=y13;

path toppost; toppost := z1 -- z11 -- z10 -- z14 -- z15 -- cycle;

path bottompost; bottompost := z3 -- z16 -- z17 -- z13 -- z12 -- cycle;

fill toppost withcolor .5white;

fill bottompost withcolor .5white;

draw signboard;

draw z11--z10--z14--z15; draw z12--z13; draw z16--z17; % signpost

x20=w-x21; x21-x20=16u; draw z20--z21; % ground level

x38=w-x31; x38-x31=8u; x32=x34=x38; x31=x35=x37;

y31=-y38=12/27h; y32=-y37=9/27h; y34=-y35=3/27h;

pickup pencircle scaled heavyline;

draw z32{z32-z31}..z34---z35..z37{z38-z37}; % the dangerous bend

pickup penrazor xscaled heavyline rotated (angle(z32-z31)+90);

draw z31--z32; draw z37--z38; % upper and lower bars

\stopMPpage

which results in: