Sort of. The USA you can claim trademark rights without a registered trademark; that's the difference between ™ and ®.

But the law follows "use it or lose it" rules. If you don't defend your trademark, then in the eyes of the court it is no longer a trademark.

Hold on, that's "defend it or lose it". Author of libcurl clearly is using the name, there are new releases coming out quite often.

My wording was unclear, yes. If you aren't defending it, you aren't using it as a trademark.

Think of the term literally; if it's not exclusive to you, it's not longer a "mark" of your specific "trade". It's just a "mark".

Fair enough.

>He also needs to have registered it in the first place.

Not true. Unregistered marks can still be defended (it's just harder).

That's why there's both ™ and ® symbols. Trademark and Registered Trademark.