It is printed on only one side (opposite of that of the year), in the upper-right and lower-left corners of the note. It is composed of a letter followed by 11 digits.
How do I find the short code? (1 letter, 3 digits, 1 letter ending with a single digit)
The short code is somewhat hidden but it can be found from the front side of the note, ie. from the same side where the year was found and opposite of that of the serial numbers.
5 €: in the far-left of the colored area, 1cm above the O in EURO
10 €: in the star, to the top-right of the O in EURO
20 €: in the leftmost star
50 €: above the hologram
100 €: the first word of the text between the window and the stars
200 €: to the right of the south-western star, written vertically