Rare Penny Red stamp with sideways wtermark The Penny Red with sideways watermark. A flawed version of the most collected Australian stamp in the world could fetch its owner up to $100,000 - barely a month after he failed to sell it on eBay for 99 cents. It was discovered recently at a rural Scottish stamp fair, then brought to the 2013 World Stamp Expo in Melbourne where it was valued. The stamp's owner has not being revealed but it is known he tried to sell it on eBay after discovering it had a sideways watermark, suggesting it had been fed into the printer the wrong way. The stamp is a common Australian Penny Red, of which more than one billion were printed early last century. The owner received no bids on his offer of 99 cents, with eBay users telling him the unusual watermark "could not possibly be real." Undeterred, the man took it to a stamp fair in Scotland, where trader Ian Perry recognised its potential worth. Perry then brought it to Melbourne's World Stamp Expo, currently being held at the Royal Exhibition Building, where philatelic experts certified its authenticity and estimated its value at $100,000. Malcolm Groom, president of the World Stamp Expo, said there could be other flawed Penny Reds out there. "They were printed on sheets of 120, so we could see a rush of people looking for more," he said. Normally you'd get 10 cents for one with the standard vertical watermark so when you discover one that's a bit different, it's an exciting little find.