On January 23, 1986, the US Post issued a stamp booklet with a se-tenant of 4, commemorating the stamp exhibition AMERIPEX ’86 which took place in Rosemont, Illinois from May 22 to June 1, 1986. One of the stamps with the main color blue had a rubber hand stamp shown. The hand stamp's wooden handle had the engraver’s surname “HIPSCHEN” engraved. This could only be detected with good magnifying glasses. According to US Postal regulations such a “signing one’s work” was not permitted, but disciplinary consequences were also not mentioned in the regulations.

Since there was a second case in the same time period, the Treasury Department ordered an investigation of the last 500 stamps issued to be checked for further such infringements.

HIPSCHEN can be deciphered clockwise from around 6 o’click to 12 o’clock