Bicycle theft is a serious business, every year between 800,0000 and 2 million bikes are stolen. This doesn't include parts stolen from a bike that make it unusable. Bike thieves often get a slap on the wrist, so this problem will not go away anytime soon. Please understand there are professional bike thieves all over the country. I had a bike stolen fifteen years ago, soon after I decided to use folding bikes exclusively ( and I stopped using locks ). I take my folding bike everywhere I go: offices, shopping, bank, library, traffic court, bus, and train. For libraries and traffic court I used a bag to cover the bike, to make sure everything would be fine. While shopping I put it in the shopping cart and roll around with it.
Stay safe and keep your bike yours!