[sokoloff]

First of all, you don't HAVE to sign anything now. It is very common in due diligence to try to chase down details like this.

If you feel like cooperating, but are just uncertain of your standing, you can sign a quitclaim assignment, essentially stating that whatever IP claims that you might have (which might be none), you assign to the new entity.

If you don't feel like cooperating, you could ask for compensation now in exchange for signing or just tell them to cram it with walnuts.