Sign-in sheets are sometimes not what you expect.
If you are demonstrating cosmetics then you might get a sign-in sheet of everyone there along with addresses and phone numbers.
If you are demonstrating Kryron, expect that names on a sign-in sheet will contain all the names but some will not be real. A deputy sheriff, in uniform, may actually be from the Secret Service, FBI, CIA, or other.
So, even with a sign-in sheet you really wouldn't know who was there so it really doesn't matter what you think you need to know about who was there - you aren't going to find out.
Bourque would not disclose attendees for competitive reasons. Some folks attending might be stepping out-of-the-box to consider this new stuff.
They only person who probably knows everyone who was there is the analyst who evaluates the film from the Chinese photographer in the bushes!