So, first, I want you to draw your attention to the photo above. Yes, the background is pink but the stamps them selves are clear. You can find these at michaels for like $13 or cheaper, just make sure they are clear. If you are a stamper, you will recognize the name Stampin' Up! Their cling stamps and many others are not clear, they are just un mounted. Now, stampin up sells clear polyester stamps but just make sure that they are clear or polyester.
Once you have found your stamp(s) it's time to find a mold. You don't want a loaf mold for this because your design won't be seen from all your bars and you don't want a mold with too many designs on it. A simple geometric shape works great!
Place your stamp design side up in your mold. you can add as many stamps as you want. Measure out how much soap base you need and cut and melt that down. Add color and fragrance. Next pour your soap into the mold. Spritz with rubbing alcohol and let it set. Once your soap is set, remove it from the mold with the stamp inside the soap. Using a pick from the pj's tool kit, a tooth pick, or just careful fingers slowly peel the stamp away from the soap! You can clean up around the edges if you want and then you are done!