invisible ink

This scan of a completely blank signature card is what the USPS offered up as proof that the customer's package had been delivered.

eBay Seller Out $1,300 And Laptop Because USPS Insists Blank Box Is Actually A Signature

A woman in California recently sold a laptop computer of hers on eBay for $1,300, but it never arrived at the buyer’s house. The seller had paid the U.S. Postal Service for insurance and delivery confirmation on the package, so she should be able to get her money back and see who signed for the package. Not quite. [More]