President Barack Obama jokingly joined in criticism of Jack Lew's signature on Thursday, urging his Treasury nominee to change it before it appears on the greenback and risks devaluing the dollar.

Lew's doodle-like eight-loop signature -- a cute but utterly undecipherable scrawl described as an "unraveled slinky" by one graphologist -- has quickly drawn more media buzz than the budget guru's politics.

Standing next to Lew and outgoing Treasury Secretary Timothy Geithner at a White House event to announce his nomination, Obama said he had never noticed how Lew, currently his chief of staff, signed off on memos.

"When this was highlighted yesterday in the press, I considered rescinding my offer to appoint him," Obama said.

"Jack assures me that he is going to work to make at least one letter legible in order not to debase our currency should he be confirmed as Secretary of the Treasury."

The talk over Lew's signature, which will be electronically printed on every US banknote, drowned out expected Republican criticisms of him as too liberal.

The stylish scribble starts off with large loops, narrows at the middle and then grows back to large circles at the end, none of them seemingly related to the alphabet.

But while some said the loops weren't appropriate for the venerable greenback, others said they would improve on the inelegant signatures of Lew's recent predecessors, including Geithner.

Indeed, after Geithner lauded his nomination on Thursday, Lew retorted: "I thought I knew you pretty well, but it was only yesterday that I discovered that we both share a common challenge with penmanship."

Meanwhile, handwriting experts sought to figure out what the slinky scrawl said about longtime Washington insider Lew, 57.

"The overall loopiness generally signals hyper-secrecy. He will carry secrets to his grave," said an analysis by Graphology Consulting Group on their website.

But, it added, "His imagination is probably as relatively large as the loops, and much of his energy is expended in the realms of abstract thinking, perhaps even religion." (Lew is an Orthdox Jew.)

But handwriting analyst Kathi McKnight told the Washington Post that the Lew doodle "indicates that he just might be the cuddly sort."

"Princess Di had very loopy writing," she added.