It is possible to add a promotional, attention-getting banner at the top of all the pages in the store. To do that, go to the Website menu, click on Store, then click on Store Settings and click to open the Personalization Options section.
In that section, there will be this message banner area shown below.  Choose a background color, if desired, and enter text, images, etc. to appear at the top of each page in the store. Then, scroll down and click to save the changes. Then, view the store to see if it looks ok or if you'd like to adjust it.
To remove the banner, click the Clear link in the upper right corner of the message banner editor, then save changes.