LGBT themes in comics is a relatively new concept, as lesbian, gay, bisexual and transgender (LGBT) themes and characters were historically omitted intentionally from the content of comic books and their comic strip predecessors, due to either censorship or the perception that comics were for children. With any mention of homosexuality in mainstream United States comics forbidden by the Comics Code Authority (CCA) until 1989, earlier attempts at exploring these issues in the US took the form of subtle hints or subtext regarding a character's sexual orientation. LGBT themes were tackled earlier in underground comics from the early 1970s onward. Independently published one-off comic books and series, often produced by gay creators and featuring autobiographical storylines, tackled political issues of interest to LGBT readers.