I often go looking on Etsy to see what my competition is up to. I have noticed many fabric postcards that have the makers name or web address. Mostly they write that information along with the USPS required word "Postcard" by hand. Although I always thought that the advertising was a good idea, that writing it by hand looks like crap.
I finally got around to having a rubber stamp made and I think my cards look a whole lot better if I do say so myself.