I found this great Sketchup design by ALX: http://sketchup.google.com/3dwarehouse/details?mid=112d9018c88671703fdfd6bc6322f73b&prevstart=0
So I exported it to STL, adapted the (approximate) real size scale, and printed the model :)
1) Print the numbered parts (I used black ABS and there was some wrapping, it is better to use PLA)
2) Fix them with glue (a glue gun works well)
3) If you have good drawing hand try to paint the letters so it looks more real :)
Thanks to ALX for the original desing and to Juan GonzÃ¡lez GÃ³mez who helped slicing the parts.
Printed on a custom Printrbot :)