Pi trademarked in US
I think there's an issue with how easy it seems to get trademarks in the US


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Idiots.

The trademark appears to be for <PI symbol>.—pi followed by a full stop - so the use of the PI symbol on its own is surely OK.

There are a lot of things that can be trademarked. T-Mobile owns the trademark on a specific mix of the colour magenta. I expect a search for Barbie Pjnk will show that Mattel owns the trademark for a certain shade of pink associated with its range of dolls.

Sounds are trademarked too - those natty little jingles in adverts,mor those tones that are almost but not quite unlike jingles. The startup chord used by Apple in its computer range (F sharp major should you wish to have a go), and the startup chimes for various variants of Windows are also trademarked.

Trademarks are generally limited to certain markets or sectors, so the PI symbol can not (currently) be used in garments, but it can be on a book cover.

Another example - the RAF had to trademark their roundel for the fashion industry because they felt it was being diluted by the recent mod inspired fashion industry. So if it's being used, it's either infringing this, a license to use is being paid, or there is a significant difference which can be demonstrated.

Trademarks is, as you can probably tell, a nightmare. I remember a company I worked for trademarked our logo (which had a kind of stylised @ symbol in it). We had to not only provide artwork, but also the colours claimed and the sectors. It didn't stop another company from bitching that we'd done it, but because their use of the @ symbol was so different to ours, there was no grounds for argument.