That's the thing isn't it.  Unless the product is a 'knock-off' of something that anyone (or most anyone) would recognize (the alien from Aliens is a good example), it requires something of a community recognition interface and diligence.  Then it requires the comparison that you mentioned to see how close to danger the knock-off is.

In the musical instrument industry, it's rather funny.  A Taiwanese company, hypothetically, can make a guitar that looks, sounds, feels, and even uses the same components of a more popular trademarked brand (say, Fender, for instance).  As long as they don't use the name, even though the rendering of the insignia is ghostly familiar, it is legal.  Call it 'Bender' or 'Fenzer' or 'Fenda' and there are no infringements.  You put 'Fender' with the same design and you're out of business.  Funny that... :)

C makes it easy to shoot yourself in the foot. C++ makes it harder, but when you do, you blow your whole leg off.

 -- Bjarne Stroustrup

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