Your headline might be "Come back to our site today for 10% off" or "We miss you." I've seen some very creative versions of these.

These banners make the viewer feel like they need closure and remind them that they did visit the site already.

They can get annoying if seen too often or for too long though so make sure you cap your frequency and duration.

You might use this campaign and then follow it up with the brand awareness campaign for the long term.