Look at their anatomy... Rather large ears, long snout, little beady eyes.
They can smell reeeally good, of course they'll eat about anything, so dependent upon what you smell like, that might not be an issue. If you smell like a cheeseburger, it could be a good thing.
They can hear well also, but hogs are noisy critters by nature, unlike a deer. No tap dancing in the stand while waiting on them.
Sight is one of their weaker senses... If they're suspicious and paying close attention on a bright clear day, they can see amazingly well.
On the other hand, I was driving down the road in the woods here by the house a few weeks back, rounded a corner and saw one trotting down the road. Whipped the front end of the pickup off the road, grabbed the shotgun and stuffed it out the window, and he just kept on coming. Dark green pickup parked across a white sand road, running, with an exhaust system that needs to be replaced, radio going, me moving all around getting the gun out.... And, he trotted up to within about 35 yards before he locked up.
I tried to wait until he turned broadside to shoot, but he spun rather quickly. He took a load of 00 Buck, and a pretty good limp home with him.
Typically, they will try to see and hear you first, then they'll sniff the air trying to figure you out.
Sitting in a stand, I'm guessing that if you sit still, they'll walk right underneath you, without a problem!!