On metal parts, cover the number with rust-inhibitor. Glass etching is a good deterrent. Thieves don't like cars with parts that can be traced. If you must leave a spare key on the outside of your car, be sure that it is well hidden. Lobby your local member of your provincial legislature for stricter rules for registering vehicles and tracking the disposition of cars that are scrapped.
Preventive measures do work and it is everyone's responsibility to do their part.
Studies have shown that theft-deterrent systems do reduce the occurrence of theft of some vehicles.