About UPC:

• Z - start/end guard bar
• Y - midlle guard bar
• n - digit from the first 6 numbers the code
• N - digit from the last 6 numbers of the code

How to use:

1. first you type the start guard bar: Z
2. first 6 numbers of your code, written as usual: 0 ... 9
3. the middle guard bar:Y
4. last 6 numbers of your code, using uppercase symbols: ), !, @, #, $, %, ^, &, *, (
5. the end guard bar: Z

Example:

Please Note:

• the horizontal lines above and below the vertical bars are there only to ensure proper spacing between bars. You might want to remove that, although it won't interfere with barscanners.
• there should be no space between the characters, fontsruct generates them this way. You'll have to compensate.(corrected thanks to thalamic)
  

With Kerning support added to fontstruct, no more horizontal bars are needed. I shall update the tutorial illustration as well.