If you have the Xenon HIDs, your headlights will be blue-white in colour instead of warm white, and there should be a yellow warning sticker (I believe it says '15,000', I can't remember without going to look at my HIDs) by the headlights on the inside of the engine bay.

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Steven Harrison

1993 300E2.8 - 196K
2001 E320 4MATIC - 86K