After Doc Soto quickly spots Nikki rocking a Golden Age Sandman t-shirt, he awkwardly tells her that he has "every issue of Sandman, mint condition." Now, the Golden Age Sandman didn't actually have his own comic until the outstanding DC/Vertigo series Sandman Mystery Theatre that debuted in 1993 and lasted for 70 issues. However, it might be a bit more impressive if Doc Soto owned copies of the characters first appearances in 1939 in New York World's Fair Comics #1 and Adventure Comics (vol.1) #40, all the way through to Adventure Comics (vol.1) #102 from 1945. Just something to keep in mind there, Alcatraz writers.
Nikki returned in last night's episode "Johnny McKee," sporting a different Golden Age Sandman t-shirt. (Where does she get these things, anyway? TeeFury?) And since IMDb lists that Nikki will also be in the episode "Clarence Montgomery," it seems the character is intended to be someone for Doc Soto to crush on and be geekily awkward around, even if actual romantic involvement never happens. However, since the shared obscure interest seems a bit coincidental, it's possible to read a bit more into Nikki and imagine that she's secretly working for Emerson Hauser, with the intention of driving a wedge for whatever purpose between Doc Soto and Rebecca Madsen.
But hey, let's just hope for Doc's sake that true Geek Love wins out in the end...