Yes, you can send just a message...
1. Create a custom offer
2. Target to any group of customers you define
3. Upload an image. Does not have to be a coupon. Could just be your logo.
4. Type the title of your message in the "Discount Name" field. Enter your message in the "Describe Offer" field. Connect to your social media site if you want to publish there as well.
5. Send immediately or pick a date/time to send.