check if cell only has letter "M", not "MS" or others

currently i use code to check for values that start with certain strings, but problem arouse when i was looking for cells that started with the letter "M". I have multiple instances of the letter "M" with can be followed by other letters. can i find only the one cell that starts with only the letter m followed by no other letters? An Example of two cells would be
MS301445
MP113555
M443229 this one being the one i want.
the numbers change all the time but the format of it does not.

Dim CriteriaC As String 'In this case CriteriaC is equal to "PE"
'some code
If Left(Range("A" & i).Value, 2) = CriteriaC Then
        Range("A" & i & ":D" & i & "").Copy
'some code
End Sub

For Each c In Range("A1:A" & Range("A" & Rows.Count).End(xlUp).Row)
    If Left(c.Value, 1) = "M" And IsNumeric(Mid(c.Value, 2, 1)) Then
        'Your code here
    End If
Next

ok i tested code and i had to make some changes. why wont it do the code following the test? i bet its right in front of me...

Sub DeviceCordLabels()
Dim MyCount As Integer
Dim DCL As Integer
Dim CriteriaA As String
Dim CriteriaB As String
Dim CriteriaC As String
Dim CriteriaD As String


DCL = 1
MyCount = Cells(ActiveSheet.Rows.Count, 1).End(xlUp).Row

    For i = 6 To MyCount Step 1
        Sheets("DEVICE LABELS").Select
        
        CriteriaA = Left(Range("A" & i).Value, 3)
        If CriteriaA = "PRX" Then
            Range("A" & i & ":D" & i & "").Copy
            Sheets("DEVICE CORD").Select
            Range("A" & DCL).Select
            ActiveSheet.Paste
            DCL = DCL + 1
        End If
        Sheets("DEVICE LABELS").Select
        CriteriaB = Left(Range("A" & i).Value, 2)
        If CriteriaB = "PE" Then
            Range("A" & i & ":D" & i & "").Copy
            Sheets("DEVICE CORD").Select
            Range("A" & DCL).Select
            ActiveSheet.Paste
            DCL = DCL + 1
        End If
        Sheets("DEVICE LABELS").Select
        CriteriaC = Left(Range("A" & i).Value, 1)
        test = IsNumeric(Mid(Range("A" & i).Value, 2, 1))
        If CriteriaC = "M" And test = 1 Then                       'both values could be true but it wont run code.
            Range("A" & i & ":D" & i & "").Copy
            Sheets("DEVICE CORD").Select
            Range("A" & DCL).Select
            ActiveSheet.Paste
            DCL = DCL + 1
        End If
        Sheets("DEVICE LABELS").Select
        CriteriaD = Left(Range("A" & i).Value, 2)
        If CriteriaD = "PS" Then
            Range("A" & i & ":D" & i & "").Copy
            Sheets("DEVICE CORD").Select
            Range("A" & DCL).Select
            ActiveSheet.Paste
            DCL = DCL + 1
        End If
    Next i

End Sub

wow... 1 does not equal true. I knew it was in front of me!