If you use the Outlook Word Editor as follows to create the message the default signature is retained and you process the message body as if working in Word from VBA.
You will need to add the code function to start Outlook as indicated

Private Sub CommandButton1_Click()
Dim TempFilePath As String
Dim xOutApp As Object
Dim xOutMail As Object
Dim olInsp As Object
Dim wdDoc As Object
Dim oRng As Object
Dim xHTMLBody As String
Dim xRg As Range
    On Error Resume Next
    Set xRg = Application.InputBox("Please select the data range:", "KuTools for Excel", Selection.Address, , , , , 8)
    If xRg Is Nothing Then Exit Sub
    With Application
        .Calculation = xlManual
        .ScreenUpdating = False
        .EnableEvents = False
    End With


    Set xOutApp = OutlookApp() 'requires code from http://www.rondebruin.nl/win/s1/outlook/openclose.htm to start Outlook correctly
    
    Set xOutMail = xOutApp.CreateItem(0)
    With xOutMail
        Call createJpg(ActiveSheet.Name, xRg.Address, "DashboardFile")
        TempFilePath = Environ$("temp") & "\"
        Set olInsp = .GetInspector
        Set wdDoc = olInsp.WordEditor    'access the message body for editing
        .To = ""
        .Cc = ""
        '.Bcc = ""
        .Subject = "MONEY FOR " & Format(Date, "MM/DD/YYYY")
        .Attachments.Add TempFilePath & "DashboardFile.jpg", 1
        .Display
        Set oRng = wdDoc.Range
        oRng.Collapse 1
        oRng.Text = "Hi Jo," & vbCr & vbCr & "Below are the numbers for today. Let me know if you have any questions." & vbCr & vbCr
        oRng.Collapse 0
        wdDoc.InlineShapes.AddPicture FileName:=TempFilePath & "DashboardFile.jpg", Range:=oRng
        oRng.End = oRng.End + 1
        oRng.Collapse 0
        oRng.Text = vbCr & vbCr & "Thanks," & vbCr
    End With
End Sub