You're right that my use of the word "proof" was a little strong. I should have said verifiable physical behavior predicted by ID that cannot be predicted without ID. But I used "proof" as a short hand.
If all things are a product of intelligent design, then it would be difficult, if not impossible, to provide a specific example where ID does not apply. The theory fits well because the physical universe is ubiquitous with intelligibility. The first indicator of intelligibility is mere existence coupled with cognition. Even in this case, function (cause and effect) is apparent. I see no reason scientifically to discount intelligent design in any case where there is cause and effect.
Science is, and must always be, a quest for intelligibile data. It is not an unreasonable inference to make: jumping from intelligibility to intelligence and design. At the same time, it is not an empirically provable idea. That is why the idea should, to be honest, be presented in qualified terms. As far as I know, that is how proponents of ID generally state their case: tentatively.
But as history plays itself out, the principles at stake in this debate have little bearing on the general body of knowledge aquired by science and scientific method. Much good has come from pushing aside ramifications that might cater to superstition and false belief. At the same time, much harm has come from cracking science up to be more than it is, namely a practice limited by human weaknesses.