I just read this article about the mysterious maple syrup smell that has plagued New York for years - I hadn't actually realized that "maple syrup smell" was a problem in New York. Oh, the things I learn. I can only think of two places that have stamped their smells onto my brain - Greeley, CO and Chicago. When the wind is blowing just right (or even when it's not), Greeley smells like cows - I was only there for a few hours, but I was told that you eventually get used to the smell. I noticed Chicago's smells most when I walked past alleys - alleys were always a blast of heavy garbage smell. I walked by alleys often, hoping to spot a rat (I was working on a paper about Chicago's rodent control program) - all I ever got was the smell, though. That, and some really great pictures of the "Target: Rats" posters.
I've noticed that Stephenville has its own smells. Mainly, I notice the smell of horses. Sometimes the source is obvious - I'm walking home, suddenly smell horses, and look up to see to my shock (hey, I'm not used to this sort of thing) that someone has a horse trailer with an actual horse parked next to a house. Sometimes the source isn't so obvious - I was once walking home (I walk a lot) and spent a couple minutes looking around for the horses I was smelling, but I never saw them.