You can contact Bill through the address below. I’m not sure whether you’ll get a reply or not but it’s worth a try! Be sure you send along a self addressed stamped envelope (SASE) for information. If you live outside the US, you will need to include an International Reply Coupon (IRC), which is available at some post offices, otherwise they won’t be able to use a foreign stamp. Good luck!
William Morris Endeavor Entertainment
9601 Wilshire Blvd.
Beverly Hills, CA 90210-5213
Some tips on writing
If you wish a photo in particular signed, send an 8×10 one along.
Be patient: replies can take anywhere from a few weeks to a couple of years! Don’t expect to receive anything right away. If something does come quickly then you’ll be pleasantly surprised, but if it doesn’t then you won’t be disappointed.
Don’t expect a personal reply: you have to realize that Bill gets a lot of fan mail, and it just isn’t practical for him to sit and answer every one. Often celebrities hire someone to handle their mail or send out photos for them. They may or may not even read your letter. Only send a letter if you feel comfortable with the possibility of never knowing whether Bill has read it or not.
Send a self-addressed stamped envelope: it’s only common courtesy to enclose a self-addressed stamped envelope when writing to someone and expecting something back. This is especially important if you’re sending a photo to be signed… be absolutely sure to include a correctly sized return envelope with enough postage so they can return your photo to you.
Don’t send anything you’re not willing to lose: it’s not uncommon for fans to send items to a celebrity to sign, but mail does get lost, letters do get misdirected, and on rare occasions people will throw mail out without reading it (this is especially true if your mail is sent to an address which isn’t the correct address for the celebrity). Don’t send anything to Bill that you would want to lose… only send expendable items.