Conway Stewart made lots of different variants of the 540 "DINKIE", starting in the 1920s up to 1942, in many different colours, with flat tops, domed tops and peak tops; with ring tops, cap clips or none at all.  This example was certainly made late in that period. Finished in marbled pink and black, it is without clip or ring top. The very clear imprint reads "   "DINKIE"  Conway Stewart London   No 540". A second imprint around the barrel is also very clear, reading: " MADE IN ENGLAND".  It has a small filling lever terminated with a round shield, with an intertwined "CS". The is a slight hint of damage to the plating on the lever The ink sac has been replaced. The clipless cap has a black peaked top and a single gold plated cap band.  

The nib is stamped "Conway Stewart  14CT  GOLD". Unusually for such a small pen, it is a broad/italic nib, so for such a small pen, it certainly makes it's mark!