I happened to be looking at this today. I picked up the following from a legal website
Choosing and protecting your brand | OUT-LAW.COM
Establishing and protecting a brand
"The strongest form of protection for a brand is a registered trade mark. Basically, trade marks identify the products or services of traders, to enable consumers to distinguish between the products and services of different traders. You will often see a brand with the letters 'TM' after it; this is to identify a trade mark of the business. There is nothing to stop you putting 'TM' after your business name or brand, to show that you are asserting rights in it as a trade mark. However, the symbol ® denotes a registered trade mark and it is an offence to use this symbol with a trade mark which has not been registered.
If a trade mark is registered, special rules apply which simplify the way in which it can be protected. Unregistered trade marks can also be protected, however, it is much cheaper and easier for a business to enforce its rights in a registered trade mark than in an unregistered trade mark. For this reason, businesses should consider obtaining registered trade marks to protect their brands. Most countries have their own systems for trade mark protection and registration."
I've been looking at whether to trademark my own new .ie site, but while in development I noticed that what had been a dormant .com site with the same name is now in Beta mode and it looks like they're registering the trademark in the US. My site hasn't gone live yet, but do you think alarm bells should be ringing?