There is a protocol when describing certain relationships to apply honorific titles. In particular when referring to Dominants (or Dommes). See, I did it just then. I capitalised the first letter. For a submissive, the lower case. I do differentiate when writing non-fiction and I would do for real people, though I have not written about real people. However, in my books? It was a dilemma. To begin with I did use capitals and then when I decided to publish my stories, I wondered how it would be perceived. To somebody unfamiliar with the lifestyle and its accompanying nuances, would it put off the reader? Appear pretentious? I would capitalise Q for the queen, G for God and other job titles, but D for Dominant?
In the end I took out the capitals. I’m not writing these books for a fixed audience of and it looked better to read. Also, my grammar checker threw a wobbly.
However, there are exceptions. I do use D when abbreviating to D/ s or Dom / sub because it defines the relationship, rather than an individual. In the same way TTWD is used for the board definition of This Thing We Do or BDSM to cover a range of activities and people. I also, when writing from the perspective of a character, such as an email or text message, used the upper case, because the character would use the honorific title in their own writings.
So, I may have offended some by my decision or perhaps it’s not that important. What I have tried to be is consistent. An important element of the D/s dynamic.