Seems easy enough to me, using the Windows version. I just hit "t" to call up a text dialog box, enter "1mA" into the box, click on the "vertical text" check box if I want the text to be vertical, and then lay it down somewhere on the schematic.
You can mess around with things a little more than that. For example, you can grab the text and use ctrl-E or ctrl-R to rotate or flip it around. But that only changes the anchor point around. You still can only get horizontal or vertical text in one form, each.
In the example you show where the current is added, the text is blue and uses even numbers (not precise ones with lots of digits.) Which means it is consistent with a text addition, like I described. Unfortunately, I don't have a mac, so I can't check it there.
EDIT: You now have two very different methods to try out, given the other post here (at this time) on this! Great!
EDIT AGAIN: On Windows, you can move your mouse over a wire and the pointer will change from a thin-lined cross to a red "probe" symbol. If you hover over the node with the red probe visible as the mouse cursor and then right click your mouse, you get an option list showing. Among the options, I see something that says "Place .op Data Label." If you select that one, you'll get the label on the node that the other answerer talked to you about.
Now, you can hover the mouse over that newly added label, see the mouse cursor change to a 'text bar' cursor type, and if you right click now you will get the display of nodes he also mentioned. (Under Windows, anyway.)
Does that help you on the Mac, at all?