I've been super sick this week, and haven't been here much, so I'm just going to spray out a bunch of random ideas and ignore me if they don't make any sense.
more free sock patterns than you will ever want:
http://www.knittingpatterncentral.com/directory/socks.php
if you go to the main directory and click on jewelry, I am pretty sure there is a pattern for sock pins. (cause, and it's embarrassing that I know this, people use them at knitting festivals and conventions to denote that they belong to certain knitting groups, No! I don't personally have one)
On another note, this would entail more volunteer labor, but the most effective way to have the socks labeled might be to have a form printed onto an iron on label or tag with blank lines for the info. Either ironed on to the back or inside the sock. You might be able to get a discount if you shop around screen printing shops (there are tons of them, someone will take pity on us!) But the point of this would be uniformity and ease of reading. So people could send in the info on a piece of paper, and then it would have to be transcribed (fabric pens are waterproof and easy to find and use) and ironed on by volunteers. It might make sense to have 3 different tags based on the info that it seems you are seeking- one for kids, one for adults, one for the deceased.
Another thought- people who are otherwise capable of decorating a sock for themselves but cannot sew will be turned off and possibly prevented from participating by the need for sewing, buttons and buttonholes. Is there any way it could be optional to make such a tab yourself, like to send it in without it and have that part done by volunteers if you are unable do that part but can still decorate your own sock? cause I really think if you ask people to sew and make buttonholes this will be dead in the water. ( Next to no one knows how to sew buttons anymore- which I know cause I've sewn a lot of buttons for people) If they don't know what they are doing, even listening carefully and with the best of intentions, there is a pretty good chance the buttons or buttonholes will be too big or too small, risking either not fitting or falling off.
Another idea is to put out the call to knitting and sewing groups when the time comes and this is launched. Many do group charity projects. The knitting group I co-founded in Maine does like 4 a year. My step mom is in a knitting group that does nothing but make shawls for sick people. The point is we may be surprised by the number of healthy volunteers we can round up. ( I personally can get at least 3 knitting groups to help, I'm certain of it, and most knitters are capable of very basic sewing)
Another thought is that if the socks happen to be handknit the tabs could also be knitted. I am only suggesting this for my sake because I know I can more reliably make the right size button hole that way than by sewing.
I haven't gotten through every single page of this yet, it's the first day I've felt up to reading much in quite a few days, so my deepest and sincere apologies if my suggestions are off- base or repeats or have already been addressed.
ETA- I'm gonna go dig through my sock yarn now. Perfect ME project...I only have to make 1!