From Anna Von Reitz
Instruction to Safely Identify Your Home and Property in the Case of Martial Law Intensifying.
Take a rigid piece of material-- wood, metal, foam core, etc. and make a sign --- a rectangle 5 inches tall by ten inches wide.
Draw a diagonal line from the top right to the left bottom corner so that there now appear to be two triangles inscribed, one above the other.
Color the top triangle black and the bottom triangle white.
Firmly attach this emblem to your house, your gates, and display in the front and rear windows of your car, boat, etc., to warn the military that you are a civilian "vessel" and that they will be trespassing on civilian property if they enter in upon your land, auto, home, etc. and will be acting against international law.
Field Manual 27-10/1956
Section 4, 45 and 46
Here is the Emblem that prints out the right size: