Here is a useful little label that you can print out and stick on a box
that you don't want accidently turned over. You can see that not only
do I have an arrow pointing up and designated accordingly, I have another
appropriately marked arrow pointing down. For purposes of conciseness,
I have used this handy abbreviation, dn.
Now, you see, if the box were upside-down, it would be immediately
apparent, because the label would look like this!