Literally 'trouble your carriage' — 驾 originally meant the noble's horse-drawn carriage, making 劳驾 a centuries-old honorific for asking a favor. Inserting 您 between them is the extra-polite Beijing flourish that 劳驾 alone lacks.
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Classic old-Beijing courtesy. 劳驾 by itself is nationwide Mandarin; 劳您驾 is unmistakably 京味儿 and sounds either charming or old-fashioned depending on the listener. Safer polite alternatives: 麻烦您 or 请问.
