Like other firms Ross produced patriotic cards during WW1. The firm was a member of the NBC Cartel.
Later cards in this series drop the RPH roundel in the logo and just use the horse, reverting to the symbol used by Heinrich Ross before his association with Rotophot. From the small number of later cards seen, cards before 5026 carry the RPH-Ross logo; cards starting with 5033 are marked only with the horse. The highest number seen is 8113. There is an incomplete catalogue of the 5000+ cards at RPH-Ross 5000 (and above) Series.
Ross, through the firm Ross Velag, produced thousands of film star and related postcards 1919-1944, of which there is an extensive catalogue on the above-mentioned ROSS site.