The most important way of communicating in Zen monasteries is through the sound of traditional instruments. One of these is the板 Han, a massive wooden board hanging by the front door of the Zendo. When Han is invited, the monastics and other Zen practitioners know that it is time to close everything they are doing and make their way to the next scheduled practice. This could be meditation, a Teishō, ceremony, etc.
The words written on the Han may vary from monastery to monastery, from Zendo to Zendo, but their main message is that life is too short to waste it on unimportant matters, and its sound is an invitation to return to the present moment.
The characters written on the Han hanging on the front door of the Urban Nun ZENDO read:
Birth and death are of great importance.
Everything changes quickly.
Wake up to every moment.
Time is not waiting for anyone.