Mb's with factory alarms have no LED Alarm indicator lights.
If it has red led's then there is an aftermarket alarm somewhere.
Look under the hood for a siren. if you find one, there should definately be an aftermarket one.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.