An infringement of a common law trademarks (™) can still be held up in most western courts such as the USA, Canada, UK and Australia, just as an example. You can still sue someone if the CL trademark is currently in use, just not to the same extent as a registered trademark (®). Registered trademarks are also protected for a period of time, unlike common law trademarks which expire when the company is defunct or no longer used.
Why does anyone give a rat's about these things anyhow? Put your spare time to better use, my friend.