I was East. I made my opening lead, and this dummy was revealed. The conversation proceeded:
East→Table: 3♥ is strong?
North→Table: special convention
East→Table: you must tell us about those
North→Table: this is our own convention
East→Table: You must tell us every time you make a bid that is your own convention
North→Table: why?
East→Table: because those are the rules of duplicate bridge
East→Table: you cannot have secret agreements
I actually think that East/West was new and willing to learn the correct procedure. Is there a place on BBO where players who are new to duplicate or to online play (but not necessarily new to bridge) can read about expected procedures?

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3♥-(p)-4♣-(p)
5♣-all pass