A small piece of info came to light today whilst reading a Bomber Command forum. All RAF stations were given a call sign. According to Code Book CD0270(3) (which came out in the Spring of 1944), Waltham's was "NAMETAB" (the majority of the call signs I have seen are all rather peculiar, but I assume this was to make them stand out more when heard). However, it does appear that the call sign for stations was periodically changed.
100 Squadron would also have had various call signs which were updated even more often it appears.