To have the join form (sign up form) on your ring's homepage, simply copy and paste the following code into your source: You have to update the ringid line toward the bottom. Where it says "FILL_IN_RING_ID" you need to replace it with your ring's id.
Site title
Description (max 250 characters)
Keywords (optional; max 150 characters)
Site entry URL
HTML code URL (leave blank if same as entry URL)
Site ID (letters and/or digits)    
Password
Do not use
a valuable
password.
Name (name of the site's webmaster)
Email (email address of the site's webmaster)