I thought when you appliquéd you used fusible interface to adhere the fabric and then stitched the edge. Or are you suggesting writing directly on the fabric? The back border is white flannel with bright paw prints. A few are black so there would be a few dead spots but its possible if the fuzzy isn't an issue.
What are laundry markers? After trying to mark with white fabric marker I couldn't see I'm learning that all pens are definitely not equal.
Will pencil show up well on the fabric? I could probably make due with the blue fabric marker I bought. It shows up ok on white, although I haven't tested on flannel. I'll probably just use block letters. My handwriting isn't anything special.