E82 135i wheel identification

[Knuckles]

I’m currently refurbing some 135i alloys, during the keying I noticed ‘13’ embossed into the wheel on the spoke next to where the little ///M badge sits.

Does anyone have any idea what it’s for?

I’m not going to lose sleep over it but I figured this is the best place to ask

 

[imprezaworks]

@Sir_Dave

 

[davo172]

Year of manufacture would be my guess

 

[Knuckles]

Why on the front though?

 

[imprezaworks]

Style of wheel maybe?