Nah, nobody ever really mentioned an honor code. I guess there was a paragraph on the cover sheets of some of the exams or something. But nobody ever really mentioned cheating, either. It just wasn't done. Over 50% of my exams were timed closed-note take-homes. For finals, there had to be some official structure, so you'd sign them out of the registrars office and had either 2 or 24hrs to return them, plus like 15min extra for the 2hrs to find a place to take them. If you started disallowing closed-note takehomes, the entire structure of finals period would change drastically!
I think it's mostly cuz it was a small libarts place with tiny classes. A) the profs already kind of knew how well you knew the material/could think, B) no curve, and C) it is really hard to disrespect a prof who you know very well - and cheating is absolutely disrespectful.
I mean, imagine going to the pub with the chem department while feeling guilty over cheating, or eating Thanksgiving dinner with their families and kids thinking "I'm thankful that your mom was crazy enough to trust me to be a decent human being," or traveling with them. One of my profs regularly brewed the beer for department events...you can't drink a man's beer and then lie to his face!