I originally signed up with my one domain. I have several domain names that I'd like to put Google ads on. Do I have to sign up again and again or is there a way to let Google know that I am interested in having my other domains have Google ads as well.
You don't sign up for another account unless you do it in another name since Google only allow one account per person. Best way is to just include your Google account number in the Adsense code for the new sites, then go to the Channel section and list the new sites (and any sub-domain pages you wish to channel). This way you can see which sites and pages within sites are collecting revenue.
You dont need to sign up again . Just use the same account with all your websites that comply with adsense TOS
You can use your Adsense account on as many website as you want. Google will notice it and have them in account. You can use a different Channel for tracking your earning from each site individually. Just keep in mind about the content. It should not be such which vialte the ToS of Google Adsense. Nuttymarketer
Once you start adding multiple domains to AdSense, you can track how each domain is doing using "channels". This will show you on a domain by domain basis how each one is doing with impressions, clicks, ctr, cpm, etc.. Good luck!
As long as you haven't assigned channels to them, you can even copy and paste the same adsense code from your previous sites on your new site and google will recognize them. Google is quite flexible in this.