Step 1: Insert a polygon and change the number of sides to 8. Dimension the octagon 6"x6"x1"high. 

Step 2: Place the workplane on the top face of the octagon.

Step 3: Insert text that is 0.5"high and change it to say "STOP".

Step 4: Insert a 5"x5"x1" octagon hole and move it down 0.5". 

Step 5: Group the 2 octagons together, making a valley in the sign for letters to sit.

Step 6: Move the text down 0.5" to be flush with the face of the sign. 

Step 7: Group the sign and text together.