Consider the following photo of the Westminster Cathedral:
What are those separator-dots called? I see them on many inscriptions. Why is it there?
It is called the interpunct.
Empty space to separate words as we do now is not a universal phenomenon. Just as well the Romans might ask why we leave space between words instead of putting a dot in between or spelling all the words together.
The dots mark word boundaries, but I am not sure if they are added more for legibility or similarity to ancient inscriptions. Following ancient conventions does give a certain prestigious feel to an inscription.
In ancient Rome one would either separate words by an interpunct or not at all. See this question for the development of word spacing.