those look like spline drive "tuner" lugs. 6 point, fairly common, i do not believe thats an actual "lock'
usually used on rims where there isnt enough space to fit a hex head lug. my winter rims use those lugs.
my guess would be the person who owned it before had a winter wheel set that came with those lugs and used them instead of the bmw lugs-- did you check the trunk/glovebox for something like this:
you can probably find it locally-- i recommend buying more than one, when used with impact tools, they sometimes split.
Past: 2001 330i ZSP/ZPP/Step
Past: 2004 S60R 6MT Sport
Past: 2007 335i 6MT ZSP/ZCW/322/655
Past: 2010 335xi ZMP/ZCW/ZPP/PPK/PE
Present: 2013 335i 6MT ZMM/ZDH/ZTP/3AG/494/508
Current Homeland Threat Level: