Oxenaar is best known for his banknote designs. In this series of child welfare stamps, he paired children’s paintings with all-lowercase Baskerville. They were issued in 1976, the year he became head of the department of art and design of the Dutch Postal and Telecommunications Service (PTT), a position he held until 1994. From 2000 to his retirement he taught at the Rhode Island School of Design. Oxenaar passed away on 13 June 2017.