I would like to share some perspective on this topic that might be helpful (disclaimer: I am not a Trademark attorney but we have helped several thousand customers with filing a Trademark).
Trademarks are filed based upon a Class and Country. It is also possible for different companies to hold Trademarks for the same name across different industries. For example, Delta airlines and Delta Faucets operate in two very different industries.
Usually domains can be a good fit for multiple industries. So even if you file a Trademark in one specific industry, it is unlikely to offer any advantage if the end user intends to use it for a different industry, or in a different country.
More importantly, when you file a Trademark, you have to file it with an "intent to use". This means you can't register a Trademark just to tie it up; you need to use it in commerce.
If you filed your trademark on the basis of intent to use, you must file a Statement of Use within a certain period of time to show you are using it to sell goods and/or services.
So unless you plan to develop the domain for your own commercial use in future, it is not a good idea to file a Trademark purely from a domain investing purpose.