Aaah, all this reminds me of the time I ran a Saab specialist retailer called Elkparts. Our logo was the silhouette of an elk which we took from an actual road sign common in Sweden. We had some T-shirts printed and offered for sale on our website. They were popular enough to attract the attention of a large US based purveyor of horrendously over-priced style-less chavwear who had a range of crappy T-shirts with a vaguely similar elk motif. We received a wonderfully threatening letter from their solicitors, requesting all sorts of damages running into eye-watering amounts for passing off, if we didn't cease and desist immediately. Had they asked nice and politely in the first instance, we might have obliged. Instead we employed a trademark lawyer who put up a good defence, along the lines of; we were using the logo before they were, so they were therefore the ones who should be accused of passing off and essentially, because we'd nicked the logo anyway, if they had a problem with incorrect usage, they should take it up with the Swedish government. In the end, after a few months of stern letters back and forth, they backed down and we couldn't afford to mount a counter-case against them, so, 3 grand lighter, we were back to business as usual. A total waste of time and money, with only our lawyer benefiting from it all, but by God it was satisfying.
Anyhoo, apologies for rambling. Good luck with it all Solar City - worth fighting when you know you're right.