What is it?
A Timelord Psychic Container is a small box used by the timelords to send psychic messages for help, they can break through timelocks and even exit the universe, they contain the thoughts of the timelord inside, so when another timelord receives it they can hear the message and send for help. These can be used in situations such as the TARDIS breaking down, getting stranded, and POSSIBLY the time war.
You can add a seal on the front of the box to show which timelord it is from, one timelord had a tattoo, which they used as the symbol on the box, however most timelords just get their name in Ancient Gallifreyan written on the box when they send it. The Writer and The Doctor have both obtained one before.