The wiki (https://wiki.openstreetmap.org/wiki/Switzerland/Map_Features) says to tag the prohibition sign with a car on top and a motorcycle on bottom as
motorcar=no motorcycle=no
. But according to the definition of access, trucks, buses, etc. do not fall under motorcar, despite still being prohibited by that sign: https://wiki.openstreetmap.org/wiki/Key:access#Land-based_transportation. So theoretically this might lead to trucks, buses, ATVs being routed over such roads wrongly.
Maybe we should just tag this sign as
motor_vehicle=no mofa=yes
, since that’s the actual meaning of the sign and the mofa=yes is the actual difference with the other, 3-way sign that bans all motor vehicles? As a side effect, it may improve rendering of walking/cycling maps, which often look for motor_vehicle=no.