When your child shows an interest in making letters, shapes and numbers, keep in mind that they may not have the small motor coordination to make the letters yet using pencils or crayons. This doesn't mean that they aren't ready to start forming the letters in different ways, though!
Using straight shapes like popsicle sticks and wavy shapes like yarn or string to form letters is another example that kids have fun with - add a little glue and some construction paper if you want to make it permanent.
Something as simple as changing the media you are using may help entice your child into spending more time exercising those muscles that they need to develop. Markers, for instance, are easier to push across paper, playdoh is a great way to exercise the fingers and even Legos and other building toys encourage the use of the same small motor skills necessary for writing correctly later on. Use YOUR imagination and see what you come up with!