Should I trademark my domain?

and if so, how?

I have a .com domain that I've built up over 4 years and it's a very successful site. I've just been to check other extensions for the name and have found that 5 have been registered by other people.

Now this is a name that was nothing until I bought it so it's not like some-one else decided on the same niche and coincidentally got the same name. 3 of the names are just holding pages, one re-directs to one of those crappy "search" pages from a typo of my .com domain and another is a "buy this name / crappy search" page.

One of the registrants is a UK based NGO and very prestigious!

What should I do? What are the dangers if I don't?

since the name _as a domain name_ is only rented, you may first wish to pay the rent for the maximum time.

I'd look at it from the other end: there are three points that must be met before a domain can be taken away. Don't know where the link is right this moment to that, though. If you can find the requirements then you'll have to be ready to use that information and strike when it is required.

Meaning: keep an eye on all of them.

======================
the answers on this link seem like a little overkill, but may be the safe way to go:
http://www.patents.com/dno.htm

Thanks for that link Herb - it seems to be the direction I need to go at least

I've read reports of cases where people wanted to take over domain names and made claims for them. When it happens to you, you have to respond quickly and state why the points of the claim don't pertain to you. Makes interesting reading if you can find the cases on the Web.

Strangely enough, I got hit by WIPO.INT this past week for the first time.
This may result in some interesting info for you for I will fight it to the max. From what I can tell, an international trademark will be the way to go.
This may get deep and set a precedence but ... so it is when you step outside the zone ( my zone).
The legal team will not be involved because I feel the charges are so full of holes that they have no leg to stand on ..... but the process itself offers up what may offer some prime defensive references.
It ( the acquisations) has not been approved by WIPO yet but the defamation presented says that it will. I've already built hundreds of pages of defense.
Hang on a couple/few weeks .... I think the "rules" are fixing to change
Hal