Hong-wu: Year 16, Month 4, Day 22
24 May 1383
Envoys were sent to confer tally-slip books (勘合文冊) on the various countries of Siam, Champa and Cambodia. These were sent in order that when Chinese envoys arrived at these countries in future, the country could verify their status by fitting their tally-slip together with that of the envoy. If the tallies did not match, the envoy would be spurious and they were then to arrest him and inform.
Zhong-yang Yan-jiu yuan Ming Shi-lu, volume 6, page 2399