POS Display
There is a POS display in the Hub, connected to the Bustracker Raspberry Pi. The model number is POS7300 2164P-LCM .
Currently, it is used to display the tag name of the card that was used to open the door and to provide a visual indication of the doorbell.

HTTP API
An unauthenticated, LAN-only HTTP API exists to send stuff to the POS display. See the code for available routes. It is available at http://bustracker2.core.devhack.net:8080
Card swipes
A Flask-based HTTP API runs on the Pi, at port 8000, that accepts text to be sent by Home Assistant (or other future sources; it has a default "fade time" on the order of seconds set so that such messages are ephemeral). The source code is available at https://git.devhack.net/devhack/door-pos-display (/opt/pos-display-api
on the Pi).