Button that Selects string "T", "X", and "R"

See the attached sample workbook. I inserted a command button from Form Controls, set its caption (text) to "T" and set its font to Wingdings 2.

I assigned the following macro to the command button:

Sub Button1_Click()
    With ActiveSheet.Buttons("Button 1")
        Select Case .Caption
            Case "T"
                .Caption = "X"
            Case "X"
                .Caption = "R"
            Case "R"
                .Caption = "T"
        End Select
    End With
End Sub

 You'll have to allow macros when you open the workbook.