Orange Book 4D4 said:
If a partnership agrees to make take-out doubles of suit bids on almost all hands with opening bid values (not just on hands that are short in the opponents suit or have substantial extra values) then this should be disclosed on the system card. Similarly the practice of doubling for take-out on unusually weak hands should be disclosed on the convention card.
The recent Portland Pairs thread had many posters arguing for a very nuanced view of what constituted an unalertable take-out double: a crude summary would be that if a double is ostensibly take-out by agreement (and might well technically fulfill the definition in OB 4H6), nevertheless if it is not a "pure" take-out double, then it should be alerted (for example, in that case, because it might, and in fact did, have competitive under/over-tones).
Now in club bridge there are a number of pairs who play "t/o" doubles in the way described in the first sentence of OB 4D4. A recent example (with no support for the other major) was:
(N/S in this example are a regular, long-established partnership who may be assumed to have a full understanding of each other's bidding style. Let's not, however, get into what might or might not be good bridge.)
Do you consider disclosure on the system card to be sufficient (assuming it is there, which is often not the case), or do you consider that the double should be alerted as well?
PeterAlan