Hi,
My commute from the UK to Holland takes me past Antwerpen, and yes, there are signs telling drivers to turn off their cruise control before they encounter the Antwerpen ring road.
However, Belgian traffic law makes it clear that these signs are intended for HGV drivers - but it would be sensible for car drivers to follow the advice. Particularly north-bound where the motorway merges with the ring road on a blind bend and then immediately plunges into the Kennedy tunnel under the Scheldt river - great idea for the driver to be fully switched on.
Elsewhere in Benelux, yes there are similar signs near Rotterdam and Amsterdam - and they seem like good advice.
Robert