Chile 2004 Official Envelope
Starting in 2002 Chile has released stamped envelopes for Christmas, Mothers Day, and Valentines Day which have been sold at the post offices with prepaid domestic postage. The value is not indicated on the envelopes but various markings indicating "prefranquero" (prepaid) have been used. All of the envelopes come with a matching sheet of paper for the message.
The 2003 Valentines Day envelopes had the prepaid marking added in black. It looks as if it was applied by a machine similar to a meter machine.