What you are seeing is most likely one of two things:
1) It's oil, which would mean it would be coming from the valve covers, or
2) It's water, which could be seeping from the head studs (IF you have head "studs"). Head studs are notorious water "seepers", BUT they are also stronger than bolts (and bolts don't leak). "Usually", on nitrous and supercharged engines, we use head studs. You can easily tell this by looking at the outer edge of the head bolts, and if they have nuts rather than just a bolt head, then they are studs. We don't always use studs on some applications, simply because if the engine bay is real tight for space and you eat a head gasket (which is fairly common when running nitrous or superchargers), it makes it an absolute hell of a job to get the heads off, because the heads must be lifted up, and over the studs to get them off the block, where bolts, you simply remove them and lift the head about 3/8" off the block (to clear the head dowels) and they're off.
Now, let me explain something here. It is entirely impossible to have oil leaking out of the head gasket! If you look at ANY Ford or Chevy head gasket, there are ONLY 2 oil holes, and they are WAY up at the top of the gasket, where oil drains back into the "valley" area of the block. This oil is NOT under any pressure at all. It is simply "drain back" oil from the rocker area. There is no oil that comes out of, or back into the block, via the deck surface... period!
Now, here's why it's impossible for oil to be leaking out of the head gasket. Between those two, small oil drain back holes at the TOP of the head gasket, you have 4 VERY large cylinder bores, (that are under massive amounts of pressure and heat), and then you have numerous water jackets that are under normal cooling system pressure (about 12-14 psi). So, how can oil (that isn't under any pressure) jump across 4 large cylinders, AND across numerous water passages, and then find it's way out of the side of the head and still look like "oil"? It's simple.. it can't! If oil got into the cylinder bores, it would vaporize instantly and make blue smoke out the tail pipe. If oil tried magically jumping across the water jackets, then it would MIX with the water and you would have stuff that looked like baby shit on the outside of the block, AND, you would have that same "baby shit" substance floating around in your cooling system.
I can't tell you how many heated arguments I've gotten into with idiots that have leaky valve covers who insist that oil is leaking from between the head and block, and I usually tell them, if that was possible, then monkeys would fly out of my ass too!
Oil flows down hill, and there's no oil above the head / deck surface area EXCEPT the valve cover rail. There isn't even any oil in the intake manifold. Yes, sometimes you can have a leaky intake manifold "end seal", but you would be hard pressed to have that oil end-up along that particular edge of the engine unless it was magic and it flowed THROUGH your valve covers. When end seals do leak, oil runs down behind or along side the water pump, and down the back side of the engine, but it certainly doesn't end-up along that outer edge. Besides, you shouldn't be using any end seals on your intake manifold anyway. You should only use a bead of silicone, which helps PREVENT a leak from occurring, where end seals can often CAUSE a leak.
Now, if water is seeping out of the head studs, this is fairly common, but it is only coming up the threads (because most head bolt holes go through the deck surface and into the water jackets) and "wicking" it's way out onto that outside edge, where the head meets the block. If you didn't know any better, you'd think water was leaking out of the head gasket, but 99% of the time, it is just seepage out the studs. This does absolutely no harm to the engine, and if it bothers you, you can put a small container of Bars Leak into the cooling system, and the seepage should stop.