Having said that, I recall Jimmy Dunn's speech at the pseudo-25th anniversary, BNTC 2004 (my report), in which he noted that the society provided a fine example of the "routinization of charisma", beginning informally and dynamically, and increasingly becoming like a formal society, with its own president, secretary, treasurer, committee and website (even if the website is currently on hiatus). Perhaps the next step in that process is for people to think of themselves as members.
Additional note: while I was secretary, the society also had its own logo, which my wife Viola designed (see above). It has since been dropped on the website, though it's perhaps worth nothing that we decided to make the logo refer to the "conference" rather than the "society".
Update (11.23): Lloyd Pietersen's comments are worth bringing up to the main post:
Two comments. First, you'll be pleased to know that the logo still remains on our letterhead. So any letters I send out contains your original logo. Second, BNTS is formally consituted as a Society and is a registered Scottish charity. It still does not have a formal membership but the committee does refer to the following criteria for admission to the annual conference:
(1) Teach New Testament (or a cognate discipline) at a recognized HEI
(2) Hold a doctorate in the area of New Testament
(3) Currently engaged in a programme of study that leads to a doctoral degree in New Testament
(4) Have previously been in attendence at the Society's annual conference
(5) By special permission of the committee for a time limited period