It's not greedy to lock out one seal, you should never have more than 2 people on a seal ideally anyways. And the reason you can lock out 1 seal for yourself is you're taking the time to make a hopefully good group.
Just don't advertise the seal you want, and if someone asks about it, tell them it's already taken.
Ya don't tell people what seal it is until it drops, great advice to elevate yourself to a douche in the group. Treat it like you would Nyzul, A,B Seals Freelot. It tells people they can get something and that if they need it they can join, while at the same time stating you want C seal so it isn't a surprise when it drops and you take it.
I mean really why not tell them what you are after that is kind of silly, and the general mindset is why people don't enjoy pugs.
You're confused and deliberately misunderstanding. It's a generally accepted convention amongst NA players that if you shout for instance. "Pallid Percy NM Do you need it? PLD SAM THF Head Seal You can have this /tell @1/4" that you're implying the RDM seal is taken, otherwise you'd be advertising it. People who respond to that shout should only need those seals, or be aware that those are the seals up for grabs.
If someone wants RDM seals it is their responsibility to ask, not to assume that RDM seals were simply forgotten and are actually free lot. They're the idiots if they get all the way to a kill without asking then get upset that RDM seals are claimed. Also it's the responsibility of you the leader to find out what seals they want before or immediately after you invite them so as to keep tabs on who wants what and if what they want correlates well with what jobs they have and what jobs you need in the future.
Nowhere in my post did I indicate you should deliberately obfuscate what seals are up for grabs. Even if I was a complete douche (pot meet kettle), and advocating douchery that's still a bad idea because you'll only get one kill on the NM and then people will leave. Not to mention you'll have a harder time forming pugs in the future.
Even amongst JP players it's very clear if you don't advertise a seal, it's not for lotting. That being said, JP generally follow the convention of marking a locked item with the 〆 character. Occasionally you will see NA following a similar convention using X but it's much rarer than simply taking the item out of the shout entirely, and it's just as clear in that way. Keep in mind that JP have a lot more room to say something in a shout.
Edit: PS: It's absolutely asinine to build a group around the "Freelot" system, especially for seal NMs where you shouldn't need more than 6 people to kill it. People are less likely to get what they want, and without organizing it to a small number per item you may end up with a lot of competition over one or two seals. If you don't actually mean free lot, and simply that the seal is "open" because no one in the group wants it yet, you shouldn't say free, you should just list it or say open or Y/X where Y is the number of players in your PT that want it and X is the amount you intend to possibly invite that want it, hopefully 1-3. Edited, Feb 6th 2011 1:04pm by RamseySylph