Engraving topic seems to be the conversion of Paul on the road to Damascus. What a nice piece. The S = John Selbing the designer. 2835 is the glass pattern as far as I know. The 1803 may be an engraving design number(not sure). The C4 = 1956, I suspect - the year it was made presumably. The RP = Rune Pettersson the engraver.
All of the above is based on the info on Page s 136/7 of the ""Orrefors - the Swedish Glassplant" by Ann Marie Herlitz-Gezelius.