Yesterday, Queen Elizabeth II unveiled a plaque celebrating the Government Communications Headquarter’s (GCHQ) 100th birthday. It was placed at the original headquarters at Watergate House when it was known as Government Code & Cypher School (GC&CS). Hidden in the plaque are two codes. After the ceremony, the Queen posted coded tweets as did GCHQ.

PS At the Watergate House, people used to send each other dessert like chocolate eclairs through the pneumatic tube system.