beside it's not allowed as per the forum rules, I wouldn't recommend posting the e-mail in a forum message or signature.
It's one of the best ways to draw the attention of spammers. Beside using it for sending spam to you, they can also send spam messages in your name with your e-mail as sender. (It's not so hard to do this.)
Of course most companies or mail providers might have now good anti spam software, but its better if the "work" of the spammers can be made useless as much at first.
Remember that you have the PM or PN function, as well as an e-mail function in your personal part of this site. So you can receive/sent those messages from/to forum members without giving the e-mail address to the public. If someone really wants to know more about/from you, then they can easily click on your name and send a personal message or e-mail through this system here. (Should someone overuse these options you can check in the FAQ of the forum what you can do)
Same applies also for other websites where you have to leave your email to get some information. Think twice if it is worth to publish your e-mail to someone you don't know. It might happen that you not only receive mails from the site you just signed up but also from other sites they gladly handed the e-mail to.
I hope this serves as some kind of help