A Puerto Rican friend having a baby in February got, as a gift, a couple dozen onesies in different sizes...decorated with the Taino (native) pictographs. Just simple white onesies, made wonderful with careful addition of brightly colored symbols with coordinating decoration on the collar, that happen to be culturally significant to the mom.
Great idea. Don't know what kind of fabric pain or marker was used, but the effect was good. I think for all the upcoming births in my friends circle, this could be a great way to do something for them.
Of course, for me it'd be geeky stuff.
Like one soon-to-be daddy is a huge Star Wars fan. I think he needs onesies with Darth Vader and R2D2 on them. Maybe a Rebel insignia, but the dad's more into the Sith.