Who has signed the item? Obviously, an autograph that is very popular and scarce will hold a high value.
What was used to sign the item? Ink, Vis and sharpie marker are king. Pencil is almost always of a lesser value.
What is the signature on? A signed photo, document or letter is always more valuable than a piece of paper or other odd item. A signed photo is next and bigger photos are worth more than smaller ones. 4. What is the condition of the signature and item? Obviously, any damage to the item or signature will lower its value to some extent. Mint condition will always bring the highest value.
How many are there? Obviously, any item that is in scarce supply will have a higher value.
Have the forgers ruined the market? Any item that has been ‘attacked’ by the forgers might also have a reduced value as many collectors who do not know how to recognize authentic material will have purchased many of the forgeries thus reducing the demand.