Hi @Kristin Ålmo!

That's a Link to icon. All objects in Miro are linkable. 

To add a link:

1. Select an object and click the three dots on the context menu.
2. Choose Link to or use Cmd + K (for Mac) or Ctrl + K (for non-Mac).
3. Insert the URL or click another object on the board that you want to link.

You'll find more information about internal and external linking in this Help Center article!

That was very helpful, thanks