Link Warning is a Greasemonkey script that will check links for you. Email (mailto) and PDF links have small icons appended to them. This is quite like QBullets, yet now we don't have to wait for webmasters to implement it.
The images used are gracefully stolen from www.jordanwillms.com.
Once you've installed the Greasemonkey script, you will see the results here.
Adobe's Corporate backgrounder, some mail link, and a regular
link.