thanks for the tip - the four groves in the safety latch - almost bought it on ebay
http://www.ebay.com/itm/Iain-Sinclair-Cardsharp-2-Outdoor-Folding-Safety-Knife-Blade-Credit-Card-/***940984964?pt=Collectible_Knives&hash=item2ec9041a84&nma=true&si=7OyHna0u%252BaXBTiejSECKc5Nnj2c%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557