As a boss once told me, trademark law requires you to be a litigious arsehole, and to act as soon as you become aware of the issue.

This may not seem friendly to you, but the default is a heartless C&D with the letterhead of a legal firm and starting something like “our client…”

FWIW it's not true. You don't lose trademarks by letting others use them, you lose trademarks by not paying your renewal fees (or genericisation: but that's actually protected against by trademark use).

This is not legal advice; this is my personal view and in no way relates to my employment.

Also not a lawyer, but it is either literally what that boss said or very close to what he said — he may have used a different expletive, but he didn’t seem to be a fan, and I have every reason to think he was sincere.

It's an oft repeated myth/excuse. I guess it lets TM management firms rinse clients for larger management fees.

Out of the blue, after 8 years..