Luke Macgregor / Reuters

Two of the first legal tender coins struck to commemorate the engagement of Britain's Prince William to Kate Middleton.

Hoping to get your hands on a royal wedding T-shirt or tea towel with Prince William’s official coat of arms? You may be disappointed.

“With the exception of carpets, cushions, wall hangings and head scarves, Royal Devices MAY NOT be used on textiles (which includes articles of clothing, including T-shirts, drying up cloths and aprons,” read the guidelines, posted on the British Monarchy website.

But have no fear; royal wedding commemoration mugs, thimbles, plates and coins can still bear the official symbol. “The guidelines don’t ban anything from being made,” said a spokesperson from Clarence House, the official residence of Prince William. “They place restrictions on the coat of arms, and the couple is content for any images to be used in any way so long as the images fall within the bounds of taste and decency.”

Guidelines on the use of the coat of arms and other symbols of the monarchy are common and issued for many royal events, including the queen’s upcoming diamond jubilee. That said, wedding memorabilia cannot be produced indefinitely, as the guidelines state that “souvenirs of the Marriage of Prince William and Miss Catherine Middleton may not be manufactured after 1st October, 2011.”

Within hours of the engagement announcement, memorabilia sporting the young couple’s image popped up around Britain and on the Web. Britain’s Asda supermarket chain was said to be the first to sell engagement mugs, and royal wedding china from the historic British china manufacturers Aynsley and Royal Crown Derby is now for sale. Even the Royal Mint is already taking orders for the official engagement coins, although the final design is still awaiting approval. Meanwhile, the official engagement portrait has yet to be unveiled.

eBay has dozens of listings for royal wedding and engagement souvenirs, including postcards, Christmas ornaments, thimbles, and salt and pepper shakers. But those hoping to make a quick buck may be disappointed: It can take years for royal souvenirs to appreciate in value, as evidenced by the eBay listings, where most items are currently selling for under $10.

"The problem with post-Victorian royal memorabilia is that was generally mass-produced, and people tend to hang on to it, so there's still a lot of it around,” antiques expert Judith Miller told the Guardian newspaper.