|Click here for related articles on Fanlore.|
Graffiti has several fannish applications.
"Graffiti" or a "graffiti wall" were often a part of older print fanzines.
Graffiti Pages in Print Zines
The graffiti was often created by the staff of the zine, and it was meant to have been the creation of the characters in the canon that was the zine's focus. For example, the graffiti in Star Trek: TOS was created by the crew of the Enterprise, or the graffiti in Star Wars by the characters in that movie.
Starting in the 1960s (and stretching into the 1970s), the phrase Frodo Lives! began to appear as graffiti on American college campuses. The phrase may have carried multiple meanings, including the belief that Frodo would not die after going into the West, that Tolkien's works lived on in his fans, and even a show of faith that Frodo and Sam would prevail in destroying the One Ring. Since not every potential reader on campus had read the book, the phrase was, in its own way, an early spoiler. It also began appearing on t-shirts, buttons, and posters and was adopted by the hippie counter culture movement of the 60s and 70s
Graffiti Boards at Cons
An example: "After supper we went to inspect the graffiti board and add our contributions. Among mine was "I need more Data -- T. Yar," to which someone later added "I need more input -- Data," ha ha ha." 
Another con, Peripatetic, had a graffiti board.
Examples of Graffiti in Print Zines
from Spockanalia #2 (1968)
from Masiform D #3 (1973)
from Millennium (1980)
the cover of Aftermath #2 (1984)