Got this response from GM (Ha - they must love me! Keep testing them!)
So, if you want to be extra-incognito, you could get Via Mat to shift bullion the 5 miles from Via Mat, Kloten, Zurich to the 'free zone' Via Mat, Zurich Airport and back again, without the LBMA 'chain of integrity' being broken. In other words, you could 'hide' it then have it re-accepted by GM, without any assaying problems.
Of course, this would all need confirming by Via Mat... And, unfortunately, you'd need min @400oz gold (a full bar) to do it. Or 30000oz (min' possession at Kloten) of silver (ahh, but GM state they won't, as yet, accept silver). However, this Via Mat situation may be relevant to Comex bars (100oz) too (Note Jim S's recent stuff about shipping to the Via Mat 'free zone' depository at Zurich Airport.