| Taram dinosaur bait |
Take the spring-loaded wrist sheath in Adventurer's Armory. Add a dagger. It's not much of a stretch to say you had one made so that the blade sticks out, rather than just dropping the dagger in your hand.
For bonus Assassin's Creed-ness, have an enchantment put on it to extend/retract the blade at will. I'd base it on Mage Hand, so it'd be pretty cheap.
I took a really long time looking for a piece of gear similar to this. I took the spring loaded heavy wrist launcher and had a tinkerer inventor gnome npc customise it so that with quick draw it was a free action to spring out but took a move action to load the blade back in the wrist launcher. My rogue fighter had the underhanded rogue talent and i talked it through with my dm that as long as the enemy hasn’t seen my blade i could get in the max sneak damage and after the enemy would be immune to The ability for 24 hours. Making the talent much more valuable if you skip the “in the surprise round” part. Hence, made sense that a hidden blade while the oppenent is unaware of its presence would be a complete surprise in melee combat. We just skipped the part of magic since my character has a special hatred for spellcasters and people who rely on magics instead of wits and strategy.