Which type of round would NOT typically be used for signaling purposes?

The use of mortar rounds for signaling purposes generally revolves around the needs of communication and visibility on the battlefield. Smoke mortar rounds and illumination (ILLUM) mortar rounds are specifically designed for signaling. Smoke rounds create a visible smoke screen to mark positions or routes, while illumination rounds provide light for nighttime operations, aiding in visibility.

High-explosive (HE) mortar rounds, however, are designed for destructive purposes, intended to cause damage to enemy forces or infrastructure rather than for signaling. Their primary function is to deliver explosive force rather than to convey information or assist with visibility, making them unsuitable for signaling applications.

Frangible rounds are designed to break apart upon impact and are used primarily for training and safety purposes, but they also do not align with the purpose of signaling in a combat environment, which is typically addressed by the use of smoke or illumination rounds. Thus, while certain rounds may have signaling aspects, HE mortar rounds are definitively not used for signaling since their objective is to inflict damage.