One of Michael Jackson's biggest fans is SO CONVINCED there's something fishy about his death ... that she dropped $16,800 on her credit cards to have conspiracy-theory banners flown all over the L.A. area ... TMZ has learned.
The message-towing planes mysteriously started buzzing L.A. 2 weeks ago with banners like, "FOLLOW THE $ TO MICHAEL JACKSON'S DEATH" ... and "LAPD -- HONOR BOUND TO TELL TRUTH FOR MJ."
Sources connected to AirSign, the company flying the banners, confirmed to TMZ ... a Hollywood costume shop worker paid for 11 flights over several locations including the downtown L.A. courthouse where Michael's wrongful death lawsuit is going on right now.
The woman, who wants to remain anonymous, tells us ... "I'm hoping that someone will look at those messages and say, 'If someone feels that strongly about it, maybe this is worth looking into."
As for the massive cc debt ... she says she can handle it because she's single and kid-free.
And in case you think she's totally nuts ... she does have one connection to MJ. The shop where she works supplied some costumes for "This Is It."