Brown sticker
Brown sticker is a category of contract bridge conventional agreements defined by the World Bridge Federation (WBF).[1] Brown sticker conventions are considered to be difficult to defend against, and thus are permitted only at high levels of tournament play. Only highly unusual methods (HUMs) have a higher classification.
A convention qualifies for a brown sticker if it fulfills any of the following criteria:
- An opening bid of 2♣ through 3♠ may be weak and does not promise a known suit.
- An overcall of a natural opening at the one level does not promise four cards in a known suit.
- A weak two-suited bid where one of the suits by definition may be only three cards or shorter.
- It is used for protection of psychic bids, or systemically required psyches.
Notable exceptions are the Multi 2 diamonds (due to its popularity), a natural 1NT overcall, and cue bids on strong hands to force partner.
In general, if a bid is weak (or potentially weak having multiple options) and does not promise four cards in a defined suit (when weak), then it is likely to qualify as a brown sticker convention.
References
^ The World Bridge Federation (WBF) definition of Brown sticker conventions in its Systems Policy manual, page 3.