The external links filter module adds a small icon to all external and mailto links. It’s great for notifying users that links are external. Requirements:
Go to http://drupal.org/project/elf and download the module and place it in sites/all/modules.
Then enable the at Administer >> Site building >> Modules.
Let’s now configure the Filtered HTML format. Go to Administer >> Site configuration >> Input formats and click on configure.
Scroll down and tick the external links filter in the filters section.
If you are having any problems check the order of the filters. Click onrearrange in the filter settings page and make sure the external links filter is second last.
That’s it, nice simple module. Remember there are extra options at Administer >> Site configuration >> External links filter.
If you have any questions just leave a comment.
Get in touch and tell me about the role or what you're building.