How to check if a range contains letter or not

I would like to ask on how to use Isletter on a Range value.

Please see below my code:

If Range("$E$52").Value = **"Isletter"** Then

    Worksheets("Offloading_Tributary").Shapes("Object 115").Visible = False

        Else

    Worksheets("Offloading_Tributary").Shapes("Object 115").Visible = True

End If

Thank you in advance.

Regards,