Best Way To Create A Banner For A Sale

Anyone have a method of creating a nice looking banner to promote a sale etc?  I'd like it visible when people log into a gallery.

I can create one in Page Designer but can't apply it to exiting galleries.

I can create a Billboard and apply it to existing galleries, but these don't scale well on mobile (text is always miniscule)

I can create a site message but this is small and will be applied to galleries that I don't want included in the sale (I'd just want to apply it to galleries within one section)

I can include a message in the Sale  within the price list but this is only ever visible when someone clicks into an image to show the product prices - if people don't click in they'll never know it's there.

Anyone have any other method?

use the earlybird space, then copy the code to every gallery you want targeted?

Yeah I don't really want to be copying things to 100+ individual galleries and then having to remove them all again when the sale is over.

In the section settings I can apply a Billboard and tick a box to apply it to all galleries in the section.  This is really good it's just the Billboards just don't look right at all on mobile.

Then you will have to use "Site Message" but you are limited to text and color background only. You can also create one for each gallery, no way to just make one banner and mass edit galleries to display it.