Which direction should the arrows point in a sorted table? [closed]

In a sorted table, it's common to have an up or a down arrow indicating the sort style. However, I'm having some trouble determining which direction the arrow should point. In an ASC sort, characters are sorted 1-9A-Za-z. Should the arrow point up or down?

I've found implementations of both on the web, so that didn't help me much: Up and Down (you have to create the table first).

Is there a hard and fast rule for this? I find myself able to justify both implementations. Which method do you use? Which is more intuitive to you and why?

Edit: Some of you have suggested alternate implementations like rising bars or having letters with an arrow indicating sort direction. Great suggestions. I'm definitely open to other options. The less ambiguous, the better. It might be picky, but I'd really like there to be minimal or no confusion on the part of the user.

Edit: I ended up going with the rising and falling bars for now. It's not standard, but seems less ambiguous than the triangles. The current sort column shows three bars, small to large (left to right) for ASC, the opposite for DESC. Other sortable columns have no bars by default, but hovering over any sortable column heading (including the current) shows bars depicting how the table will be sorted if that column heading is clicked.

I don't think of them as arrows, but as a visual mnemonic of the current state. So, showing a triangle pointing down shows descending order. It is visually in line with the icon with the largest item (base of the triangle) at the top of the list and the smallest (point of the triangle) at the bottom.

I've always went with the following:

• Ascending -- Arrow pointing up
• Descending -- Arrow pointing down

In my opinion, the visual representation of the arrow pointing up/down most accurately explains the sort order.