Nick points out

: For some people stealing your design, just a nicely written letter from a
: lawyer stating the potential ramifications of failure to cease and desist
: will be sufficient to scare them off. With others you may have to be a
: little more persistent.

Actually, sending a letter requiring them to cease and desist does have
at least one other major effect that I forgot to mention in my earlier
post. Under British case law (ie. how the courts have interpreted the laws
in previous cases), if you allow people to copy your designs without taking
any action against them, then to all intents and purposes your copyright
lapses and anyone else under the same jurisdiction can feel free to copy
not just the same design, but any other. If, on the other hand, you can
point to any action at all that you have taken to enforce your copyright,
even if it was unsuccessful, then you still have a case against other
people copying your intellectual property.

So it may well be worth at least taking the first stage of an action,
even if you have no prospect of it being economically viable to pursue
it.

Another point is that although you may have to do something to "register"
copyright under US law, that isn't necessary under the international
copyright conventions, or under most countries' implementations of them.
The fact that copyright is implicit possibly has something to do with
needing to be seen to take some action to enforce it for it to remain
useful. No doubt case law differs in each country where you might want to
take action...

Andy