Imho the costs of removals are well worth the money. That's kind of the SBB's strategy, and what works better. Security can help but it can't be anywhere and anyway it can't be healty to have security staff anywhere. I'd go for:
- If possible, don't put the train in service, take another, even hide it in a depot. If not,
- get it removed ASAP (hours, not days),
- never ever leave out one to go around for weeks, months or years. Not even the smallest.
This seems to be the best way to get rid of graffiti. I had a legal one made once: when I had to pay for the spray cans I understood why it is effective to immediately remove them...
When I worked for New York City Transit (back in the bad days of 100% graffiti scarred trains), that was the general approach that we took to successfully eliminate graffiti from trains and stations.
1. Don't call it "graffiti" or vandals as "graffiti artists." We used the term "vandals" and encourage media to do same.
2. If a train had graffiti and it couldn't be removed during terminal cleanings (at the end of a line), the train was removed from service immediately. And it would be shunted into a maintenance depot for immediate graffiti removal.
This required a major change to the corporate culture which was to "make service" at all costs.
3. Never let the public see that vandalized train. Deny the vandals the pleasure of the public seeing their destruction.
4. Make sure all graffiti is removed. Don't allow even a shadow or trace to remain.
5. Bolster security. Attack the problem head on using interdepartmental task force.
6. This was applied on a car/trainset by trainset basis. Starting with one trainset, and eventually converting each trainset to "clean car" status until the entire fleet assigned to that subway route was clean.
7. Move onto a new subway route. Repeat, until the entire fleet is clean.
8. Never let up. Like cockroaches, vandals are always attacking the system. If you let up for a moment, it will snowball back to the bad old days.