I'm related to a whole string of English nobles- Earls, Dukes, Kings, Queens, the whole lot. I've also found quite a few ancestors (all related in some way to those higher-ups) called 'Sir' or 'Lady'. Does that mean anything, or is it kind of like being called 'Gentleman'?
An example would be 'Mary FABIAN, Lady of Compton', or 'John HORD, Sir of Shropshire', or 'Alice BULKELEY, Lady of Beaumane'. Is it something significant? Or is it just stating where they came from?