In case the police gotta know, rollin' it up in traffic

from Big Sean (Ft. Chiddy Bang & Wiz Khalifa) – High Lyrics on Rap Genius

Meaning

If the police don’t know by now, they will once they find smoking in his ride.

The first part of the line goes with the end of the last line. He hides his weed now because he got caught in NC.

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