VCS-7 were employed spotting for the guns on D-Day and beyond, and were not equipped with suitable aircraft at that time, having floatplanes. A small number of RAF Spitfire MkVs (6 IIRC), with uprated engines were supplied. The '4' was the unit code, with individual codes 'X', 'V', etc.
The only 'French' connection is the caption on one pic, presumably from a French publication, stating 'Squadron VCS-7', in French.