I'm going to try out a used American Deluxe Strat tomorrow, and hopefully buy it if it looks/sounds good. However, I wonder how I can make sure that the pickups are the stock SCN ones, and not something the owner replaced them with. Would it say it on the pickup anywhere? Should I look for some specific sounds to signal that they've been changed?

Could be very hard to tell, I don't think fender pickups are marked anywhere that's easily accessable. If they've been replaced with some brand name pickups it might say on the cover, but it might not. If you really wanted to I guess you could take the strings off, take the scratch plate off and have a look and see if there's any obvious resoldering. I don't think you'll be able to tell just by listening to them unless they've put actives or single sized humbuckers or something in there that's going to be obviously not a normal fender single sound.