As for references, some time ago one of our users has requested a new feature that looks quite similar to your idea.
He would like to have the option to hide all references in the model, leaving all the tables visible. If you'd like to hide selected references only, you can post your comment here:
http://support.vertabelo.com/topic/792344-option-to-hide-all-references-and-leave-only-tables-displayed/
You can also upvote this idea. The more votes the idea gets, the more likely it will be implemented.

If you mean a reference between the columns in two separate tables, here it is a short tutorial:
http://support.vertabelo.com/topic/438421-how-to-create-a-reference/

Yes. As long as you use Vertabelo for educational purposes, you can use Academic account.
Since your email domain include "edu", your Academic account will be created automatically, without any additional formalities.
I have just switched your personal account with a trial plan to a free academic account.
Enjoy Vertabelo!

In Vertabelo, we have implemented the crow's foot ERD notification, and unfortunately this kind of notification doesn't use diamond shapes.
But you can use notes to add some comments to your diagram.
You can place a note above a reference line or next to the table, and type anything you want within this note. For example, this way you can describe interactions between two elements of your diagram.

Ok, I already know what's wrong. You have registered for a trial account plan, while the option of switching plan to academic one is available only for users of a free account plan.
But don't worry, we switched your account manually. Now, you should have the academic account plan.

We don't have "non-commercial plan" (we no longer offer such accounts). At the moment, we have Academic plan only. It can be used for educational purposes only by lecturers and students (we don't call this "non-commercial" since this plan can be used by non-public universities and colleges).

Here is a step-by-step instruction how to convert a free or paid plan into academic one:

1. Click "My account" in the top menu bar:




2. Click the "Manage personal account plan" button:





3. In "Manage personal account plan" panel, go to the bottom of the page. There's a section "Academic account plan". Click the "Request Academic plan" button on the right:





4. When being in the "Request Academic account plan" section, select an appropriate option ("lecturer" or "student") and the rest of the registration form will appear. You must complete all fields, and then click the button "Confirm". After that your account plan will be changed to academic automatically since your email domain was added to our academic domains "white" list.



Note that this account can be used only by student or lecturers learning/teaching databases, SQL or related topics. It mustn't be used by non-commercial or non-governmental organizations.

If you have any problems, do not hesitate to contact me via Support.

Carina, your student domain is now whitelisted. Try to change plan to academic and let me know if you succeeded.