Ex-Warrant singer Jani Lane was carrying a note in his pocket on the day he died which read, "I am Jani Lane." But TMZ has learned Lane wasn't the person who wrote the note.

Law enforcement sources tell TMZ that Lane had no official ID on him when his body was discovered at a Los Angeles motel on August 11, and we're told he hadn't been in possession of an ID for a while.

We're told the note contained a phone number for a person close to Lane, and police contacted that person after Jani's body was discovered.

Law enforcement sources tell TMZ that investigators have confirmed the note was written by one of Lane's friends -- and that person had placed a similar note on Lane in the past. Cops have been in contact with that person.

However, the note has infuriated members of Lane's family, who tell us whoever had written the note was clearly aware that Lane had a substance abuse problem and should have helped Lane seek treatment instead of simply tucking a piece of paper into his pants.

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It's unclear if the same person who wrote the note also checked Lane into the Comfort Inn, but sources tell us it appears the room where Lane was discovered was not purchased by Lane himself.

Law enforcement sources tell us there is no criminal investigation into the death, and so far, investigators believe Lane's death was either accidental or due to natural causes.

An autopsy has been completed and results from the toxicology tests are expected soon.