This cartoon by Dave Brown from The Independent is based on an old music hall joke: "What's a Greek urn (i.e., earn)?" "About 30 shillings a week" (or some other sum of money). Music hall jokes traditionally begin with one half of a double act asking a question beginning with "I say, I say, I say", and the other half delivering the punchline.
The joke depends on the fact that 'urn' and 'earn' are homophones, and "What's" could be a contraction of "What is" or "What does". So the question is understood as "What does a Greek earn?" rather than "What is a Greek urn?" (an urn is decorated vase).
The cartoon shows French President Nicolas Sarkozy asking the question, and German Chancellor Angela Merkel (portrayed as a merciless and treacherous Sphinx) replying "Even less than now if they want any help from us!"
The cartoon relates to the Greek debt crisis. Angela Merkel has reluctantly agreed to another bail-out of the debt-laden Greek economy, but in return she will be expecting the Greeks to tighten their belts even further.