You can make a text3d object a child of a texture quad. Here, the text object is slighly offset the quad in the z direction so it can be seen clearly.
Press the spacebar to change the message
Code:
import viz
viz.go()
# Create surface to wrap the texture on
quad = viz.addTexQuad()
quad.setPosition([0, 1.5, 3]) #put quad in view
# Wrap white texture on quad
quad.texture(viz.WHITE)
#create text object and make it a child of the texture quad
text = viz.addText( 'message', quad )
text.setScale(.1,.1,.1)
text.alignment(viz.TEXT_CENTER_CENTER)
text.color(viz.BLACK)
text.setPosition(0,0,-.01)
#press space bar to change message
vizact.onkeydown(' ', text.message, "new message")