Here are a couple of fantastic pieces I traded with obviousfront at atcsforall.com. Both are thick plastic postcards which obviousfront has made and engraved himself.
The orange one was made for me and the yellow one was made in 1993 and was returned to sender after sitting in the San Gabriel, CA post office for 13 years.
These Industrial Strength postcards created some problems for the US Postal System. Several branches refused to accept them after an automatic sorting machine was damaged trying to process one.
The third photo shows the engraving machine being used to create my orange card.