[kluck]

I like the analogy.

> ...will your having ignored that sign make a difference in their interactions with you?

For sure.

> How about if you've both ignored that sign and come in wearing a disguise?

Not if he finds out. But the disguise will make it even worse if he does find out.

So it boils down to: Can you hide yourself good enough to not beeing detected (includes beeing detected by showing information that is presumably crawled rather than detecting the process of crawling)? It is a risk that you may take by weighting assumed loss (court case) and gain (money from using crawled data).

I may add: A clever "data provider" will inject some hidden beacons into their data that makes it easy for them to later detect that data in other websites. So actually you can always be detected, because you must have crawled that data from them.