[Typo3] External URL in menu

[Claudio]

Dmitry,
thanks for your reply

> I do not know easy way but I would just search of I could add image to
> this menu item showing that this is external link.

This is not exactly what I'd like to get, but in case a better solution
can't be found I'll try your suggestion.
Just I miss something: how can the above be applied only to "External URL"
type pages, and not to other types of pages linked in the menu? 
Thanks again

Claudio