In this article, I would tell you how to highlight links referring to other sites or external resources. I will give you two ways to do that.

Solutions:

Use External Links module

Download this module here: http://drupal.org/project/extlink

The module finds external links in the content and mark them with a special sign.

Use CSS for external links

You can mark external links with tag with a special style:

HTML:
<a class=”extlink” href=”External’>http://drupal.ru”>External link</a>
CSS:
a.extlink {color: red;} /* Highlighting with red*/

You can also configure appearance of external links from there.

Summary

External Links module makes the same changes but automatically. If you think many users will add external links, it’s better to use the module. If only one author publishes articles, there is less external links or you need a special highlighting of them – makes sense to make all necessary things in CSS. This way you will also reduce server loading.