Hi ilzho. I'd be really surprised if there are any silver certificates out there, but you never know. I don't look through stacks of bills myself, but besides error notes you could look for interesting serial numbers like
- star notes - have a serial number that begins with a * instead of a letter
- radar notes - serial numbers that read the same forward and backward, e.g. 12344321
- birthday or anniversary notes - e.g. 03171974
- low serial numbers - 9999 or less, lower the better
- ladders - 12345678
- repeaters - 12341234
- binaries - 21221211
- or anything that interests you personally.
Good luck!