If it's a good bike, a bike thief'll know what it is no matter what you do to make it look like crap.
I see a lot of couriers and commuters with taped up cannondales and speshies and wonder why they bother. It just makes it more obvious.
In your case, if it's just a cheap commuter bike then go with a decent D-lock and/or chain and take the post out. I doubt they'd make a real effort for something inexpensive.
Most cheapies get nicked because they're usually locked up using crappy cable locks or cheap skinny chains.