Alerting of doubles
From the blue book....
'Suit bids that do not show the suit bid'
Alert, unless the double shows the suit bid.
The number of players(ranging up to European champions) that do not understand this apparently simple 'rule' is astonishing - I think it may be helpful to reiterate it in a future ebu magazine with some examples(eg double of pass/correct 2H to multi showing t/out of hearts)