Incredible how many bicycles are stolen, because of insufficient safety measures. Easy enough to install: (1) Use of two bike lock chains. One to secure the seat (which gets easily removed) together with the rear wheel, and/or helmet. One to secure the frame and the front wheel (if it can also be easily removed) to a fixed bike store facility.
(2) When cycling take your bike papers with you including the Serial Number. So, that when your bike gets stolen you can call in with the details incl. Ser.#. I also always have a photo of my bike on me together with the documents. That is what I do.
[ http://www.cpic-cipc.ca/index-eng.htm ].
Small tit-bit: During hard times or war, when bicycles are valued at a premium, many governments resorted to treating bicycle theft as a criminal offence.