The notice for the signup bonus coupon isn't there anymore. Apparently they took it down* since sometime yesterday morning when it was up.
I have a cached copy in my browser history, though.
And no, I didn't sign up for anything since I'm still not sure I want to join the romance club when I don't read romance anyway and they don't really have enough in the historicals section to interest me (but I might still do so anyway, to support the idea of DRM-free low-cost memberships in principle and maybe they'll add stuff I have a reasonable chance of liking).
ETA: Google cache says I'm not imagining things:
YES! Sign me up for the Discover a New Love Newsletter and get 15% off my next order still there as of April 13th.
I'd write a politely worded disappointed letter to the Sourcebooks people asking about this with a link to the above, and perhaps hint-dropping that you were recommending people sign up for the newsletter and consider the club because of the bonus discount offer, and maybe they'll reinstate it.
* They did this on purpose, I'm sure, now that I finally went and mentioned it after it's been there since the start of the site launch. 