Excel VBA - Does Sheet Exist

[Hack]

I can do

If Blah = True Then
     Sheets("My Sheet Name").Visible = True
End If

And that works fine, but I want to alter this to check whether or not the sheet even exists. I don't know what it does like, but I can tell you it does not like this

If Sheets("My Sheet Name").Name = True Then

So, how to I determine whether or not a sheet exists in my workbook?