Stamp with the letter(s) or word(s) of your choice.
A few words about stamps and stamping polymer clay—
There are a variety of options. With the recent popularity of stamping, you have your choice from all sorts of alphabet sets, as well as stamps of words and phrases. Traditional, wood-mounted rubber stamps, unmounted rubber stamps, clear acrylic stamps, metal stamps (typically used for stamping metal, but also useful with clay), address stamp sets—these and other commercially available stamps are excellent choices. You can also make your own word stamps from polymer clay or using tiny (uncooked) alphabet pasta. As a final resort, you can “carve” polymer clay—before curing, with a ball stylus or needle tool, or after curing with linoleum carving tools.
If you plan to sell the work you make using stamps, you need to research the copyright rules of the companies that created those stamps. Each company has its own set of rules as to how its stamps may legally be used. Even with so-called “angel stamp” companies, which allow the sale of some arts and crafts created with their stamps, copyright policies vary. However, if you are using stamps to make items for yourself (or gifts), you needn’t worry about copyright.
Consider using a release agent with your stamp. Though not always necessary, a release agent makes it less likely that the clay will stick to the stamp, aiding in the creation of a clean impression. Water, cornstarch, and baby powder are popular release agents. Applying the release agent is as simple as spritzing the stamp (or clay) with water or dusting it lightly with powder. Whether or not you use a release, always be sure to carefully, gently wash the stamp after use. Doing so will help your stamps last for years to come.