Most graffiti vandals are tagging for recognition among the crowds interested or participating in graffiti. However, none of the vandals want their identity revealed, and they will go great lengths to avoid identification. Knowing this can help deter graffiti if you plan accordingly.
My Graffiti Removal Guy's favorite graffiti deterrent is the "SMILE You're on Camera" sign. When vandals see this sign, they tend to assume there are cameras and they'll keep moving. This way, you get some of the deterrent value a camera offers without the high price of a quality surveillance system. No matter if you've been a victim of graffiti vandalism or not, signs like these should be visible around your property. The benefit far outweighs the cost here. If these signs only stop one out of five vandals, you've already reduced your graffiti removal cost 20%.
You can find these signs by doing a simple Google search; they range from $10 - $50 each. Make sure you get them durable enough to stand repetitive cleaning as they may be a target of vandalism in the future.