What is the best way to provide trademarking information on a logo to a client after you have delivered their new logo design?
In the US, you can go to the Patent and Trademark Office:
2 things in particular are useful:
The trademark search - horrid interface, but lets you find which names and logos might be similar. Used this a lot when searching for name.
Application = self explanitory. Haven't done gone through this process. I'd recommend at least talking to a lawyer if not having her handle the whole application.
You could either point them to the place where they need to file for it (depending on your country of origin) or to a lawyer that specializes in trademark.
In Canada, you will need to go through the Canadian Intellectual Property Office (CIPO)