Just a random idea I had whilst watching the movie Helvetica.
FontJamming is related to stenciling and graffiti. It is where one goes around and alters signs to read the same, but in an ALTERNATE typeface.
Jamming is intended hint at both musical jargon of improv and freeform as well as technical jargon of blocking.
The alternate typeface may be a glaring alteration, or a subtle change, leading to "something changed, but I can't put my finger on it" reactions.