Among some players, the lead of a strengthening card when an honour is turned, is a call for trumps to be led through that honour at the first opportunity, but it is not good play.
Passing a certain winning card is regarded by most players as an imperative call for trumps.
The discard of any card higher than a Seven is known as a single-card-call. Even if it was not so intended, it is assumed that a trump lead cannot injure a player with nothing smaller than a Nine in his hand.
Answering Trump Signals. In response to partner’s call, a player should lead the best trump if he holds it; one of the second and third best if he holds them; the highest of three or less; the lowest of four; and the fourth-best of more than four. Holding any of the regular high-card combinations in trumps, he should lead them in the regular way in answer to a call.
After a Force. If the player is forced before he can answer the call, he may indicate the number of trumps originally held by playing them in this manner:—
With 3 or less; trumping with the lowest; leading the highest.
With 4 exactly; trumping with the 3rd-best; leading the highest.
With 5 or more; trumping with the 3rd-best; leading the 4th-best.
These methods of taking the force must not be carried to extremes. For instance: A player holding K J 10 2, would hardly be justified in trumping with the 10 to show number. Some experts, holding the best trump with at least four others, will not lead it; preferring to show number first, by leading the fourth-best. Others, holding four, lead the lowest after trumping with the third-best.