My suggestion would be a single speed bike because they don't look as flashy(in general). Bolt on parts such as hubs with axle nuts instead of quick releases. They do make quick release skewers that have-basicly a removable release tab. I've seen a guy that covered a 4 thousand dollar bike with burlap sacks so people thought it was trash. I'd also go with a cable lock that you can run through both wheels and the frame to the bike rack. That moslty eliminates any issues. Beyond that, you only have to deal with jerks that cut your tires or serious theifs with big cutting tools. As for the seat-- there's a devise that can be put in the seat post, then has a plug on the other end that is held in the seat tube by the bolt for your water bottle cage. You could keep the quick release seat for quick adjustments, but still be secure. If you wanna get very detailed, you cen get stem bolts and such replaced by tamper=proof torx bolts or some other security screw that requires a special key to remove. Those keys are much harder to get than your standard allen wrench and would greatly minimize missing parts or loosened bolts.
