The guidon for a mounted company of the signal corps is of the same shape as the cavalry guidon, of orange with two flags crossed of white with red centers in the center and the letter of the company in white above them. Each aero squadron carries a guidon of orange silk with the insignia of the signal corps in white and red in the center, the number of the squadron above the insignia in white and a white eagle with wings spread below the insignia. Each telegraph company carries a guidon similar to the one for the aero squadron except that in place of the eagle there is a design representing forked lightning. The guidon for each field hospital organization and ambulance company is of the same shape as the cavalry guidon, of maroon color, having in the center the insignia of the hospital corps, a caduceus, in white, with the number of the organization above the insignia and the initials “F. H.” for field hospital or “A. C.” for ambulance company in white below the insignia. The guidon for a motor truck company is a pennant, triangular in shape, of red, white and blue, the white portion being diamond shaped with one of the horizontal points at the staff and the other at the outer end of the pennant, the triangular portion above the white diamond next to the staff being red and the corresponding triangular portion below the white diamond being blue, with the quartermaster corps insignia in blue at the center of the white diamond. The flag of the Geneva Convention, to be used in connection with the national flag in time of war with a country which was a signatory of that convention, is a white flag having a red Greek cross in the center. It is used to mark hospitals, hospital ships, field hospitals, ambulances and ambulance vessels and boats. The size prescribed to mark general hospitals in the United States Army is 5 feet hoist (high) by 9 feet fly (wide) with the red cross 4 feet high and 4 feet wide and the arms of the cross 16 inches wide. The smaller Geneva Convention flags are of the same general proportions. An interesting development of warfare resulting from the increasing use of aircraft in war is the use of distinguishing marks for the aircraft of the different nations. At first the national flags were used for this purpose, but it was found that they would not serve to identify the nationality of the aeroplane or dirigible airship when viewed from all directions and another system of distinguishing marks has been adopted.