As pointed out by Daedalus in the comments:
...unless I'm reading the wrong agreement, you aren't allowed to do that on site you don't own.
Here are some of the relevant parts of Amazon.com's Associates Program Operating Agreement that support that (additional bold emphasis mine):
“Your site” means any site(s) and software application(s) that you own or operate and link to the Amazon Site.
Description of the Program
The purpose of the Program is to permit you to advertise Products on your site and to earn advertising fees for Qualifying Purchases (defined in Section 7) made by your end users.
Links on Your Site
After you have been notified that you have been accepted into the Program, you may display Special Links on your site.
and it goes on like that several more times throughout the contract.
I am not a lawyer, but since it's most certainly the case that none of the Stack Exchange sites are "your sites", there's a very good chance that you may have violated your Amazon contract by essentially spamming your affiliate links on someone else's site, in which case Amazon might very well terminate your agreement.