Registered trade-marks are designated with the ® symbol, and regular trademarks with the ™ symbol.
Even if something doesn't have the ™ symbol next to it, if it's it's a name or logo that's used to identify a product that is being traded, then it's still a trademark nonetheless.
e.g. If I copied the gamedev.net logo and sold my own forum subscriptions using that logo, then the real gamedev.net could sue me for trademark violation, even though they haven't used the ™ symbol.
Simply putting "international trademark registration" into google will give you information about how much registration costs -- Likely between $100-$1000 per country.
Generally only very big brands, like Coca Cola use registered trademarks.
Note that regardless of whether a trademark is implicit (no ™ symbol displayed), explicit (™ symbol displayed) or registered (® symbol displayed), if someone violates your rights by copying your name/logo, the only thing you can do is hire a lawyer and start a lawsuit against them...