Squarespace Announcement Bar
Have you checked out the Squarespace announcement bar? If not, it's certainly worth taking a look. In the past we've installed other 3rd party notification bars for clients such as Hello Bar and Bannersnack, which do offer some advanced options (along with a fee), however your Squarespace site has a pretty capable alternative built right in!
See how to enable and style the Squarespace announcement bar in the video below.