Whether or not this is the correct portion of the forum for this type of insignia is open to debate but I will say in advance that the volunteers of the American Field Service were considered by the French army as technically under its control and jurisdiction.  If the moderators feel that this is not the correct forum I will acquiesce.  Be that as it may, here are a few example;

 

This first is a "Union" or "Columbia" Shield hat badge.  This insignia was worn by ambulance volunteers of the American Ambulance Hospital of Paris during 1914 to early 1916 when it was replaced when the ambulance service came under control of the French Automobile Service. 

After falling under the control of the French Automobile Service, the Transportation Committee of the American Ambulance Hospital of Paris adopted a new insignia for wear on the caps of their drivers.  Examples of this device being worn on Adrian helmets is substantiated by documented examples and period photographic evidence.  The style of ht device was issued in two finishes.  A gilt finish which was worn by officers and Section Chefs and a subdued bronze finish for ordinary drivers.  This style hat device remained in use by the American Ambulance Hospital until 1917 when it was federalized by the United States Army and the American Red Cross.  

 

The first example is a gilt finish and the second is the common version.

In mid-1916 as tensions between the staff of the Transportation Committee of the American Ambulance Hospital of Paris and the Directors of the Field Service of the American Ambulance reached a zenith, the two organizations separated and the American Field Service became its own independent entity.  To distinguish itself from its former parent organization, the American Field Service adopted its own unique insignia.  This insignia went through a series of changes and evolutions over the next year and a half, until the AFS was federalized by the United States Army in late 1917.  Note on the examples shown how the use of the term "American Ambulance" is dropped in favor of the Union shield design and the logo on the banner "Service Aux Armee" is replaced by "American Field Service" in the final example.  

 

Caution needs to be exercised as these and the earlier badges illustrated have been faked extensively.   

Excellent examples of a set of rarely encountered badges.  I think it is appropriate to post these in the French section as these medical services were indeed considered French at the time.  Similar to American pilots serving in the French Air Service wearing French uniforms.  

 

Following in this thread I would like to share another example of a very uncommon badge.  This is a service badge awarded to ambulance drivers of the American Ambulance Hospital of Paris.   

These two pins were worn by nurses and volunteers of the American Ambulance Hospital of Paris.  

Outstanding badges, thanks for sharing these photos.

 

Paul