There are generally two schools of thought when it comes to autographs.
- Autographs/sketches/etc. actually deface the comic and if anything hurt the value of the comic book.
- Autographs might add nothing to a little (or a lot depending on who signed...i.e. Stan Lee), but they would have to have a COA (certificate of authenticity) from a reputable company certifying they in fact did sign the comic.
The age old question always rules in that a comic is only worth what someone is willing to pay for it.
On ComicBookRealm.com we do not track autographed comics separately (unless the comic only comes signed). When adding a comic to your collection you can check the box to indicate that it is signed and then leave a note as to who it is signed by.