Google _hint is simply keywords in google adsense code for telling google about what information is given in article or contents. It is the way for showing targeted ads in any web page.
Google is providing this facility to very few and famous webmasters who has different varieties of contents. But google is not giving this code to every webmaster. Its parameter will show like below
Reason is given on Ask Dave Taylor .
“To confirm, I emailed the Adsense team and asked them for an explanation, and here's what they explained:
So do not add this code this is against TOS. For targeting the adsense, you have to write only google title and article which have lot of keywords whose ads you want to show in your article for better CTR.
Google is providing this facility to very few and famous webmasters who has different varieties of contents. But google is not giving this code to every webmaster. Its parameter will show like below
google_hints = 'qualities husband, marriage, love’ ;
Reason is given on Ask Dave Taylor .
“To confirm, I emailed the Adsense team and asked them for an explanation, and here's what they explained:
"The feature you're referring to is one of several new features the Google Adsense team is currently testing for a very limited number of publishers. At this time, we are not able to offer these features to other publishers. Should we offer these features to additional publishers in the future, we will be sure to notify you at that time."
So do not add this code this is against TOS. For targeting the adsense, you have to write only google title and article which have lot of keywords whose ads you want to show in your article for better CTR.