Scrapers generally operate by crawling serps. They want to Scrape sites that are ranking well in the serps for the terms they are targeting. They search Google and Yahoo and MSN then crawl and scrape the sites listed there for the keywords they are targeting. They dont generally crawl sites and search for pages to scrape as they would end up with pages added to their sites that DONT rank well and could hurt the scrapers ranking. So if you dont want to get scraped you have to avoid any top ranks in the search engines :1circling
Thats why I have my links posted in sigs. From an SEO standpoint its an excellent way to get backlinks from well ranked authority sites in your niche. (Assuming you are posting at boards related to the topics your sites cover)