Square Brackets at end of Property or Method

What is the significance of the square brackets at the end of methods or properties? For example, I have a GpsSerial object "gps". When I type gps. up comes the pop up window showing all the methods and properties for that object and at the end of each will be either [O] or [M]. From VB6, I might guess that [O] is an optional argument, but I cannot imagine what [M] is.

[M] - Method.
[I/O], , [O] - Property. ex: TextBox1.Text = "sometext"
- Input only. You cannot read the value, only set it.
[O] - Output only. You cannot write to this property. Only read it.

OK, thanks.