The 1991 190E 4-cylinder (likely a M102 engine) doesn't use easily visible timing marks on the harmonic balancer in the same way older, simpler engines did. The ignition timing is controlled electronically by the engine control unit (ECU) and is not adjusted mechanically via a distributor.
Therefore, you won't find traditional timing marks on the harmonic balancer that you can use to set the ignition timing. Any adjustments to the ignition timing would be done using diagnostic equipment that interacts with the ECU.
