The most commonly-seen Grissom autopen pattern has the "Gus" formed in one pen stroke. Seen used on items from 1962 through to 1965. Note that when used with a fine pen (as in the third example below) the tail stroke of the "G" of Grissom almost touches the end of the "Gus" before looping back.
This second Grissom autopen pattern has the "Gus" formed in two parts. Used in 1965 & 1966 at least.
Whilst fellow Mercury astronaut Alan Shepard relied heavily on his secretary to sign items on his behalf, Gus Grissom apparently preferred to have the Autopen machine deal with most of his autograph requests. There are exceptions however and, whilst not as common as Shepard secretarial signatures, Grissom secretarials do exist.
All the examples I've seen to date have the same distinctive style, as can be seen in the selection on the right.
These signatures all have distinctly squat "G"s, little more than twice the height of the rest of the letters. In Grissom's real signatures the "G"s tower over the rest of the letters.
The "r" of Grissom in these secretarial signatures starts at roughly the level of the bottom of the preceding "G". In Grissom's real signature the "r" starts well below this level.
Another secretarial tell is that the dot of the "i" tends to be added high above the signature, well above the level of the tops of the "G"s. On Grissom's real signatures the dot is rarely positioned so high above the letters.