Barack Obama's speech yesterday to the US public on the Libyan crisis has been hotly debated throughout the globe.

It is a reminder that when it comes to world politics, people always take notice of what the US president has to say, whether they agree with him or not.

US presidential memorabilia has similar prominence among global investors in political collectibles, with Obama items selling particularly well.

Obama's signature can command huge sums at auction, especially when combined with White House headed note paper.

An iconic Change poster designed by contemporary artist Shepard Fairey, in support of Obama's 2008 presidential campaign, sold for £4,560 in 2011 at Bonhams in London.

Shepard Fairey's £4,560 poster

Birth certificates of US presidents are a niche market among political collectors, although those looking for an Abraham Lincoln certificate will be disappointed as certificates were only formally introduced during the last century.

Obama's own certificate is a thorny issue, with some opponents claiming that the president was born in Kenya and not Hawaii as is widely accepted, thereby making him ineligible to serve as president.

The whereabouts of the birth certificate are unknown, although a Kenyan birth certificate purportedly of Obama has twice been removed from auction on eBay. A real specimen would likely achieve a vast amount at auction.