When Sky Captain and Polly surface in the lagoon/swamp on the island, Polly notices the reflection of the number on Sky Captain's plane says 'Polly' (the audience is also shown this). The camera then cuts to the plane to show the number is 'h11-od'. However the true reflection of 'h11-od' would actually be 'yll-oq' you'd have to be looking at the reflection on the water in a mirror to see 'Polly'.