Thanks to Mauricio's excellent ruby-wmii, it's now possible to script the wmii window manager in Ruby! I noticed a battery monitor was included, but a wireless signal monitor wasn't, so I wrote one.
plugin_config["wireless:wireless"]["interface"] = "ath0"
plugin_config["wireless:wireless"]["interval"] = 5 #change if you disagree with this default
from "wireless" do
use_bar_applet "wireless", 400
end
Enjoy.