That is an endorsement. Notes are bought, sold and traded, and the process entails endorsing the note in favor of the new owner. It is comprable to endorsing a check which is made payable to you to someone else. It changes the ownership of the obligation, but not the obligation.
If is often true however, that the secondary mortgage market is often sloppy about the details, and at times are sufficently sloppy that a properly defended case can prevent foreclosure. There have been some particularly good decisions coming out of some Ohio courts.
There are attorneys who specialize in foreclsoure defense and financial services litigation. Check the web site of the National Association of Consumer Advocates, www.naca.net to find someone there who specializes in foreclosure defense.