On the underside of the trim piece toward the outer end, not quite as far out as the visor mount, there's a hole going straight up. At the end of the hole is a Phillips-head screw that goes up into the header; that's the one you need to remove. It may take a bit of probing around to be able to engage the screw head with your driver.
'97 SL500, 40th anniversary edition
'04 Olds Bravada (SWMBO's)
'06 Lexus ES330
'89 560SL (sold)
SL--Anything else is just a Mercedes.
(Kudos to whoever said it first)