Today I tried posting with a signature. I tried using a signature which was under 120 characters, as stipulated, but containing about 55 carriage returns. The carriage returns did not appear, which was half what I expected, but what surprised me was that the sig on posts which had already been posted would change when I updated my sig in my preferences. In other words, unlike USENET, I can change my sig after the fact.
Not that I ever use a sig. I just wanted to see what would happen. I mainly wanted to see how hard the McQuary-like limit on