Preprinted signatures - that is where the signature is printed into the photo, lithograph or document - are often more difficult to spot than autopens. Unless you recognise the signatures as common preprints you really need to examine the piece up close to be able to spot a preprint.

One thing to look for is pen indentations as these are usually absent from preprints. Unfortunately, sometimes real signatures with felt-tip pens or fountain pens leave little or no indentation either. There also exist, albeit rarely, preprints that are machine-stamped onto a print in such a way as to leave an indent. In these cases though there will normally be no natural variation in the depth of the indentations.

Another thing to look out for is differences in sheen/finish between the ink of the signatures and similarly-colored areas of the background image.

Of course both these things can only be verified in-person, which can make buying items at online auctions something of a gamble.

Preprinted signatures were commonly-used on certificates of appreciation and prints given to NASA employees and contractors in large numbers as thanks for their efforts in a particular project.