What is used to show that letters were dropped in a contraction?

An apostrophe (') is used to show that letters were dropped in a contraction.

Here are some examples:

* can't (contraction of "cannot")

* don't (contraction of "do not")

* I'm (contraction of "I am")

* it's (contraction of "it is" or "it has")

* they're (contraction of "they are")

* let's (contraction of "let us")

The apostrophe takes the place of the missing letters.