Thanks for your post, but this appears to be a quote from a Confederate Veteran Magazine ad, vol XIX, reunion announcement: “Medical Officers Army and Navy, C.S.A. - Our place of meeting will be the chapel of the First Presbyterian Church, centrally located and easily accessible by the display from the front of a yellow flag, the hospital insignia of the Confederate Army”
The deferent Armies of the North and South used both yellow & red hospital flags, it depends on the time period, Army and department of the Army. In general, the Medical Service from the North used yellow flags, the Medical Department in the South used yellow flags but the Ambulance Department used red flags for their field hospitals, both north & south. On the regimental level, it looks like it was up to the regimental surgeon on which color was used in the field or camp.
It’s confusing but it depends on which Union Army, Confederate Army and time period. Generally, the major hospital’s in Cities or Towns used a yellow flag. Field hospitals used red but it depends on which service or department the Doctor was in. The Ambulance Department, both North & South used red flags for their field hospitals (or aid stations) but again the time period of the war is a factor.
Hope this helps.