"What's troublesome is the loss of deterrent value," the retired general said.

Prosecutors, he said, think the case is in the public interest because of its "broad general deterrent value."

Yet the deterrent value of the fine, at least on its own, is uncertain.

He said a longer sentence would have no deterrent value.

It reduces response time, but that has little deterrent value - crime victims typically wait 20 minutes or more before calling police.

"I know we disagree on the deterrent value of capital punishment."

No one has yet demonstrated any clear deterrent value for the death penalty.

This needs to be addressed, along with whether the demonstrated deterrent value of nuclear arms might work to prevent conflict among other countries.

"You can't calculate sentences simply by their deterrent value," he said.

It's too early to say whether the decals will maintain their deterrent value when they become more common.