Use the image gently
The Rainbow Bridge can be comforting, but not everyone reads it literally. Keep the language open: together again, always loved, or waiting in the light.
Good formats
Ornaments, small display pieces, and printed cards work well because the theme is symbolic. Jewelry can work if the design stays subtle.
Pair it with a real detail
A rainbow theme feels less generic when it includes the pet's name, a favorite photo, or a phrase the family actually used.