When I requested information from Bowker about the Createspace ISBNs, she included the following note:

Also, since your website is for cartoonists, they should also know about the ISSN, handled by the Library of Congress. While the ISBN is for books, the ISSN is for comic books in the classic magazine sense. (Graphic novels get ISBNs; typical comic books get ISSNs)

As she notes, this wouldn’t apply to the graphic novels or comic-strip collections that most of us publish, but I thought it might be worthwhile to post it into the record in case the topic arose at some time in the future.