Watched brother in law just pull his to vertical in a 59 plate Audi TT at the weekend. BMW have instructions in their manual to move the wipers to vertical. Sorry, can't help with Mercedes other than turn off ignition when wipers are vertical as #2
I was wondering the same thing but my manual (C63S) says just turn the ignition off, which I find astonishing given other manufacturers actually put a feature in to do this (my previous two Audi's for example).