Yes, they sure do.  An original Singer bobbin case now costs over $100, and they can be snatched and pocketed quickly, so they are easy to steal and re-sell.  I have never had one stolen off one of my machines, but I very rarely use my machine anywhere except home.  But I have heard of them being stolen from shops, shows, etc.  And you know, there are a LOT of ornery people out there.  There are replacement bobbin cases out there that sell for less, but some people have bought faulty ones that are not manufactured to original Singer standards.  

I got a FW at an estate auction a while back and the auctioneer said he had the bobbin case up at the desk because they were so frequently stolen.

Wow good to know. Who would think that theft of a bobbin case is so common!!!

Looks like you are enjoying the upcoming restoration of your new machines.