The "This is spam" button was definitely a part of your old Norton AV. Outlook 2007 has a built-in junk email function, but it is accessed by right-clicking on the message and identifying it as Junk E-mail. There's no one-touch button for it.

The button was in your Outlook toolbar because Norton AV comes with an Add-in for Outlook. This Add-in allows Norton to scan your email for viruses, in addition to filtering for spam.

-SW