I was coming back on the train
from New Haven to Manhattan a few years ago
after I had given a guest lecture to her class at Yale.
She and I got to discussing "tactical media,"
or media that can be used to subvert the message of
more officially sanctioned media.
I told her that I thought it would be cool to quickly write a message onto a poster, by sweeping some fast-printing device over the poster to transfer some text I'd just thumb-typed into my cell-phone.
I figured that my device would only need to lift/drop five pens, like this. I implemented the applet on this page during that train-ride, on my notebook computer, to show what the typeface might look like if you "type" by dragging five pens along a line while turning each pen on and off.
An alternate version would use a small spinning hex mirror to turn a laser pointer into a portable instant message projector.
Instructions: Click on the window. Then type something.