Hi Mickey. All it means is that they have a County Parish Holding number (CPH) - which registers the land for agricultural use and allows them to keep livestock. A lot of people have started adding "registered smallholding" to the estate agent's details because it seems to attract a bit more attention from would-be smallholders.
Don't worry whether the places you're looking at have or don't have a CPH - all you need to do to register with Rural Payments Agency (Welsh Assembly here in Wales) is fill in a form. You should get your number within about a fortnight if they're not too busy. It doesn't cost anything. If the place already has a CPH, you will still have to apply, as it needs to be YOUR CPH, registered to YOU. However, don't be surprised if you get the same number!
To answer one point above, the fact that a holding is "registered" does not mean that the land automatically carries entitlements to the Single Farm Payment. This is a completely different step to getting a CPH. A CPH is required if someone wants to claim the SFP - but applying is a separate step, so don't confuse yourself at the moment.
Once you have your CPH, you'll be able to start buying your sheep, goats, pigs, etc, or whatever else you want (you don't need it for poultry/ducks, etc.). You will need to apply to Animal Health for your flock and/or herd number. Again, this doesn't cost anything. Lots of people apply for this before they get their animals, but you have three weeks from when the animals arrive to get it. Easiest thing is to get it beforehand.
If you want to message me with any specific questions, feel free. If you want me to send you a step by step guide from my book, let me know.
Good luck with your search.
Liz