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.
A few examples of preprinted signed items are given below but for more examples for individual Gemini or Apollo crews you should use the "Crew Autopens & Preprints" menu on the left.
The Gemini poster shown above right has very convincing looking signatures (see details below) but unfortunately these signatures were printed onto the posters, which were given to those that worked on the Gemini project.
This set of preprinted Mercury 7 autographs was originally part of a collectors book of space patches, complete with a genuine
embroidered NASA vector patch attached above the signatures. The signatures are quite convincing (being printed in different inks) and this page
is frequently seen separated from the original book, at which point many people make the mistake of thinking they are genuine signatures.
One of the most commonly-seen preprints is a large (16x20") 'signed' image of the Apollo 11 crew, shown above.
This facsimile cover was created by Fleetwood as a copy of a real crew-signed Dow-Unicover. This is stated on the reverse but if seen in an action listing with only the cover shown it can be very deceptive.
Certificates of appreciation, given out to NASA employees, commonly had preprinted signatures like the examples above from Apollo 16 and Apollo 17.