LURK MORE (also LURK MOAR) is the standard response to any post displaying ignorance of an established meme, or just plain ignorance. Variants such as "More, motherfucker, do you lurk it?" are seen rarely.
The userbase of 4chan has grown tremendously since its original incarnation in October of 2003. Once being comprised solely of goons and friends-of-goons, it branched out almost immediately to take on a life of its own. However, after it was resurrected from death in August of 2004, the drastically increased user base showed signs of decay. Users preferred to use names and tripcodes rather than post Anonymously, causing unneeded drama over identity theft when the value of the stolen identities was debatable to begin with; the perceived median age of the average poster dropped from college-age to high-school freshman; spelling and grammar became intolerably atrocious; users started to openly defy the rules and begin posting invitations to invade other forums or harass users over instant messenger; basically, users ceased to lurk and began to wrongly assert that they "mattered" or that they had unique identities which were more important than the traditional institution of posting as Anonymous. People began to regard the name of the poster to be of more value than the content of his posts, and the idea of always posting with a name was wrongly practiced—the exact problem that spurred the creation of 2ch and Futaba Channel in the first place.
True to /b/ form, the phrase LURK MORE has transformed into a somewhat overused meme in and of itself. Any user who is not 100% familiar with the most obscure 4chan in-jokes and asks for an explanation is often told to lurk more, regardless of how reasonable an expectation that might be. Worse still are those who advise people to lurk more and then proceed to offer inaccurate explanations for memes, meaning they themselves ought to take their own advice. This is becoming more and more common as /b/ grows in popularity. In a sort of perverse retaliation, longtime /b/ posters are beginning to deliberately spread misinformation to further muddy the waters.
Since the list of 4chan memes was moved here to the LURKMORE Wiki, from WikiWorld, LURK MORE has obtained a double meaning: it now can also be construed as an instruction for newbies to come here and look up unfamiliar memes.