Add a trademark policy for the SolidCraft name and logo

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -131,7 +131,8 @@ them: read [DISCLAIMER.md](DISCLAIMER.md).
 
 MIT OR Apache-2.0, at your option. Developed under the
 [clean-room contribution rules](AGENTS.md); third-party code and assets retain their
-documented licences and attribution.
+documented licences and attribution. The licence covers the code, not the name and logo: see
+[TRADEMARKS.md](TRADEMARKS.md) for how to name a fork or a product built on SolidCraft.
 
 SolidCraft is independent. Behaviour is designed from public documentation, general CAD
 conventions and user feedback. Reference tests use analytic values and open-source tools.

TRADEMARKS.md

@@ -0,0 +1,36 @@
+# SolidCraft name and logo
+
+The code is yours to use under MIT OR Apache-2.0 (see [NOTICE](NOTICE)). The name is not part of
+that licence: "SolidCraft" and the SolidCraft logo identify this project and the builds its
+maintainers publish, and Tangency Labs, which maintains SolidCraft, uses them as its trademarks.
+Neither licence grants rights to them.
+
+This page says how you can use the name. It is meant to be easy to follow: most uses are fine.
+
+## Fine without asking
+
+- Saying what your work is built on: "based on SolidCraft", "a fork of SolidCraft", "works with
+  SolidCraft", "SolidCraft plugin for …".
+- Writing, teaching, reviewing or making videos about SolidCraft, including in titles.
+- Redistributing unmodified official builds under the SolidCraft name, for example in a Linux
+  distribution or package manager.
+- Using the logo to link to the project or to show that something supports SolidCraft.
+- User groups, meetups and community spaces about SolidCraft, as long as they don't look official.
+
+## Use your own name
+
+- A fork, a modified build or a product built on SolidCraft needs its own name and logo. "SolidCraft"
+  may appear in its description ("based on SolidCraft"), not as its name or the main part of it.
+- Don't use names or logos that could be mistaken for SolidCraft, such as "SolidCraft Pro",
+  "SolidKraft" or a lightly changed version of the logo.
+- Don't imply that SolidCraft's maintainers made, endorse or support your product or service unless
+  they do.
+- Don't use the name in domain names, app store listings or social media accounts in a way that
+  looks official.
+
+## Questions
+
+If you're not sure whether a use is fine, open an issue or ask on [Discord](https://discord.gg/FtU4NQNVDH).
+For anything this page doesn't allow, ask first; we're generally happy to say yes.
+
+Other companies' trademarks named in this repository are covered in [NOTICE](NOTICE).