date stamp noun, verb
■ noun [C]
1
a date that is printed on sth, especially an envelope or a food product:
The date stamp shows the letter was posted yesterday.
2
a device for printing the date on a document 
- Picture at OFFICE
■ verb [+ obj] date-stamp
to print the date on a document, an envelope or a food product:
Food items must be date-stamped to make sure the oldest stock is used first.
The proposal was date-stamped 23 August 2003.
date-stamping noun [U]