PC LOAD LETTER
I remember back in the olden days when we didn't have any space and everything needed to be abbreviated or put into obscure symbols. We had eight characters for file names, plus a reserved extension. So, for example, on disk, this photo might have to be called "APTC6010.BMP".
And, years had to be saved in databases as "82" instead of "1982" because space was expensive. I think what happened, is that we all got in the habit of being obscure and obtuse because of that. We've since passed that habit to newer generations too, so that today, even when there is room available, we still do the "PC LOAD LETTER" thing instead of just being nice and clear.
This cap footprint, pictured to the left, does have a polarity indication in the silk screen. Either that, or the silk screen had some printability issues and was cut off on one side. It's probably positive up, but just to be sure, why not put a little + sign on the positive side to remove that bit of ambiguity. There's plenty of room on this board. If space was tight, I could see leaving it off, but what's wrong with a bit of extra safety when you can get it?
Baseeball been very very good to me