How to add a button that jumps to an external link in the content type?
nofollow: Links to an unendorsed document, like a paid link. ("nofollow" is used by Google, to specify that the Google search
  spider should not follow that link)
  
  source: HTML  rel Attribute


All you have to do is write your link like this:

&lt;a rel="nofollow" href="http://www.example.com/something"&gt;Buy Now&lt;/a&gt;