There should be two components ... 1) an ovular seal (~125x75) and 2) the words "National Association of Private Investigators" (~225x75)
The ovular seal should include a graphical element that has law enforcement iconography (eg. sheild, star, badge etc) in the center and a border with "National Association of Private Investigators" wrapped around.
The words should standout on a white background but not appear to flashy. Just imagine how it will look in the template noted above.
The ovular seal will be re-purposed for other uses and should look decent in black and white as well