It is probably the key fob battery but here is the list of all BMW dash symbols and what they mean...although now that I have looked through this rather large PDF I don't see this "key" symbol on the left of your display.
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991.1 GT3
SOLD: e92 M3 6MT, Jet Black/Black
Dinan: Software Tune | CF Intake | Exhaust | Pulley Kit | Stage 1 Suspension | Pedals /// BBS e88 18x9.5 et19; 18x10.5 et19 on PS4 265/285 /// Lux Angel Eyes
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