If you find out a third party is copying your brand, trademark registration provides an effective way of stopping them. A trademark registration gives you legal grounds to approach the copycats and ask them to stop using your brand name/logo by sending them a cease and desist letter.
If a third party doesn't use an identical brand name but a confusingly similar one, there might be a way of stopping them. If the goods and services between the two brands are very closely connected, you might have the right to approach the third party and ask them to stop using such a brand name. However, these situations are case-dependent, and they have to be assessed on an individual basis.