help:privacy mode
Privacy mode hides your upvotes and favorites from other users. Privacy mode can be enabled with the "Private favorites and upvotes" setting in your account settings.
Enabling privacy mode requires a Gold account. If you don't have a Gold account, but you already had privacy mode turned on, then you can keep it on as long as you don't disable it. If you disable it, then you'll have to upgrade to a Gold account before you can turn it back on again.
Note that Admins can still see your upvotes and favorites, even if you make them private. This is for the purpose of detecting vote abuse and upvote botting.