Form C.

C at the top of the form in the middle.  Rectangle is xx mm by yy mm. Printing number and date in the lower right corner outside of the rectangle.

Form C5. The C5 designation is an UPU form number.

1964. Notice of delivery of registered letter sent to Germany.

Form CN 07.  The CN 07 designation is an UPU form number.

2001. Notice of delivery of registered letter to Turkey.