By means like A band, or a TV-Show, but liking a friends status, without commenting on it brings nothing to the conversation, and could mean a variety of things. By default it should be assumed that those who ignore the CONL rule are pathetic stalkers, or hapless button pushers with nothing constructive to add, but just about have the restraint not to shout "HEY LOOK AT ME, I WANT TO BE NOTICED MORE" in public.
"Andrew likes your Activity"
The only possible reply to this is posting "CONL", with the usual reply being "whats CONL?" Thereby engaging normal communication.