If you want to, you can make a lot of steel disapear, even if you've got a small frame. I'm 5'8", 140lbs. I can hide my Project 1 while dressed only in a T-shirt and shorts.
My Project 1 lives in a Scott Hendrix SB-1 kydex sheath, I like this sheath because it is solid and has lots of eyelets.
What I do is take the black paracord that was the lanyard of my knife, feed it through the eyelset at the tip of the sheath, and tie a knot. Then when I put on my belt, I put the paracord loop around the belt after it goes through the first belt loop, and then do the rest of the belt as per normal. Stick the knife and sheath in the left pocket, handle down. Put on your T-shirt and leave it untucked. To draw, yank on the paracord that's not in the pocket, and out comes the knife. Draw it from the sheath with the right hand. Not the fastest, but it is low-profile, and you'll be able to produce it as quickly in a real altercation as you could any other knife/carry system. Yes, I've seen the quickdraw rigs. I've also been in fights. Nothing is coming out until you make an opening, or if weapons are drawn BEFORE the fight ensues. In that case, pulling a 13.5 inch long knife when your adversary presents his folder or boxcutter will certainly have an effect. "That's not a knife, this, this is a knife!"
Not that I wear shorts public...
Now, since I really wear jeans, t-shirt and jacket whenever I go out(I live in Florida. The heat may bother some, but never me, though sometimes, like during heavy manual labor, the jacket might come off), I usualy wear it in a shoulder rig made with the same paracord and sheath. Honestly though, since I don't have a permit, I usualy just pack my folder.
Does anybody know how to do a "Dundee rig", do they really work? I've experimented, but haven't been able to get it to stay in place.