The first step is to build the sign shape.  I like to use simple shapes built in the XCS software. I used the square with rounded corners and rotated it 45 degrees. I then added a rectangle for the sign post.

for this sign, we are creating a simple intersection icon for the sign.  To do this I simply used two rectangles to intersect.  An important note is that where the two rectangles intersect, there will be a square that will get engraved twice.  I selected both rectangles and used the combine tool to unite them.  This makes the icon one vector.

Finally, I used super glue to bond the base to the sign post. Then slide the two base parts onto the post,  You may also want to add some glue between the two plates.