Find your profile page. Click on "in forum". When that page appears, send your eyeballs way to the top of your computer where you always type in the http's and the www's. There will be a URL (page address) stretching across that long white box. The last number in that line is your sign-up number. Mine is 14,000 something.
Hope this helps. I was buffaloed on this a long time ago because I never thought of looking higher than the page itself.
Leni