Q. How do I tell my guests about my registries?
A. Word of mouth, it's the only way.
I promise - your guests will ask your mom, future mother-in-law, bridesmaids, etc about where you are registered. If your guests are technology savvy, they will search your name on The Knot or WeddingChannel.com and have everything at their fingertips.
Do not include your registry on any written communications you send to your guests, not on your save-the-dates and certainly not on your invitations. If a guest asks you where you are registered, you can, of course, tell them. If you have a wedding website, it is acceptable to add that to your save the date (most registries are linked to websites, so if your guests explore your wedding page they will find your registries).