Here are a couple different Baby posters, both with the Hepburn FDC (Scott #4461) along with the Grant stamp (Scott #3692) and each with a different international stamp--a snow leopard from Afghanistan (c.1985) and a Zanzibar leopard from Tanzania (c.1984).
It's interesting that Grant looks like Clark Kent--though in a female's robe--in one of the poster's illustration, but in the opposite one, he's rendered like his more debonair self and nothing like how he appears in the film.
The back of the cards have Grant's FDC on one, and the FDC of the screenwriting stamp of the American Filmmaking series (Scott #3772a) on the other, with Grant piggybacking on that postmark. There's also an FDC of the Connecticut stamp (Scott #3702) from the Greetings from America series, the oldest of all the FDCs depicted here. Note also that the home Post Office for the Hepburn stamp is in Old Saybrook, CT, where Hepburn was raised and the state where the film takes place.