Really there is no way of "preventing" recasting if you are going to be in the business of "selling stuff you made". Some Jacka$$ will inevitably recast it... usually poorly.
The best you can do is develop a network of people (here is a decent place to start) that are trustworthy... again this is a hard thing to do takes time and you will not make a lot of money... and deal within that group of trusted folk. the issue with that is that its very difficult to develop trust or even "know" someone via online methods... its just too impersonal. People can be fooled in person relatively easily, online its just that much easier.
If you sell it on ebay you're cooked... It will go to asia and all bets are off...
If you sell it to another artist you're less likely to get burned but still no guarantees... It really is a
cr@p shoot, where you are relying on peoples integrity, and honesty.
Myself I do not buy anything that is recast even if it is a good deal. When I first started this hobby I bought a few items before I realized what recasting was and that they were not the "source" of the product rather that the person selling to me was essentially stealing...
Placing a tell on a piece will only give you the satisfaction of being able to prove that origianally the source was you... which is little satisfaction when you see your work being ripped off.
Then of course there is the whole copyright debate... wher if your making a version of something in a movie that has a copyuright you're ripping them off in the first place... which I consider to be Legal and technically correct, but pretty lame. If you spend a years worth of weekends building something - its yours IMO, even if inspired by a copyrighted work.
Its a shame really as this board was developed on the premise that the people here ahd a passion for and the requisite skills to figure this stuff out and create what are essentially works of art. This place was at one point a clearinghouse of information exchanged very freely, until it got big enough where the leeches found it and started hanging around... now while its still a good place on the net, the "vibe" is different, with good reason... You can still develop a network of trusted folk to work with, and sell to, but it will be a lot harder. I wish you luck.
Jedi Dade