Box sign option has disappeared

Hi Lisa, 

Welcome to Box Community and glad to help!

Please make sure you have Box Sign enabled in your Box instance. 

To change which of your users have Box Sign enabled or disabled:

1. In the left sidebar of the Admin Console, click Enterprise Settings.
2. In the top bar, click Box Sign.
3. Click Edit Configuration from the Configure Sign section.
4. Select the enablement option.
   • If you enable or disable Sign for select users or groups, type the user names, email addresses or names of groups you want to allow or deny. 
5. Click Save.

As an Admin here's how you could configure Box Sign. 

Hope it helps!