If you earn a commission from a link, you have to disclose it. On Pinterest that means a clear disclosure in the pin description, and on any page the pin links to.
“As an Amazon Associate I earn from qualifying purchases” is the standard wording for Amazon Associates. Put it before the link, not buried at the end.
Don't rely on a hashtag alone. A disclosure should be plain and readable by someone skimming quickly.
When in doubt, disclose. It protects your account and it builds trust with the people who follow your boards.