Pit Stop Safety

Weble's post got me thinking about caravan security...if you have a pit stop, ie motorway service stop for a bite to eat/cuppa etc...do you put your hitch lock on? We don't bother but have heard some stories about vans being stolen whilst people did this as it could be easy to un-hitch and hook up to steal your van. We sometimes make our own cuppa and grill a bacon sarnie ourselves in the van when stopping and equally sometimes we can't be bothered and get something at ridiculous prices for convenience. What are your thoughts?