Lettering is a way of decorating pottery that can add a graphic and literary quality to your work. 

There are a number of ways of writing on your pottery.  You can either carve the letters into the clay using a carving tool or another implement that feels comfortable to you.  Or you can use letter stamps.

If you are good at calligraphy, freehand writing your own lettering can look fantastic.  Equally, using letter stamps can give your pottery a vintage typeset look. 

With some letter sets, you can snap the letters together to form words in a perfectly straight line.  This can be effective, as positioning the letters evenly on your pottery can be tricky.  Nevertheless, slightly wonky letter can give your pottery a handmade charm.

It’s best to use the stamps when your clay is soft leather hard. 

Also, you can highlight the lettering by painting underglaze over the letters and wiping away the excess before it’s fired. 

This is similar to the Mishima technique described above, with the underglaze color picking out the details of the recessed lettering. 

Reference -  thepotterywheel.com -