A handwritten, signed letter by Barack Obama is exciting political collectors and autograph hunters the world over.

The rare letter, which has a $10,000 estimate, is the star attraction at Hammer and Block Auctioneers' sale in Miami this evening, with many investors likely to be paying close attention.

Obama sent the letter in response to a 2009 fax from the consignor, Tim, which complained about bonuses handed out by financial services group AIG.

Tim's fax, which he fired off in hope rather than expectation to the White House, was titled: "TO ANYONE WITH ANY COMMON SENSE".

A week later he received a handwritten note on White House stationary, which read: "Tim, Thanks for your letter. I share your sentiments, and we are moving as quickly as we can to restore some common sense to the financial system. Barack Obama."

Obama is thought to read 10 letters a day from the public

Speaking of his surprise at obtaining a reply, Tim commented: "This is a very rare letter as it is handwritten on the White House stationary.

"It's well documented the president reads about 10 letters a day from folks like me, and rarely will he actually reply to them so personally."

A private sale of another Obama signed letter on White House notepaper recently achieved $6,000.