When Hillary Clinton told her audience at a rally in Las Vegas on Thursday “Here’s what I believe,” she punctuated those words with not just a vocal flourish but a physical one. Up went her hand, placed over her heart.

It’s a gesture unfamiliar from her past campaigns, but it’s a favorite this time around. In Columbus, Ohio, and Omaha, Mrs. Clinton spoke of her late father, and up went her hand, placed over her heart.

At the Democratic National Convention, when she took the stage to wild applause, she cued the audience on how grateful, moved and humbled she felt by putting her hand to her heart, once, twice, then a third and fourth time.

It’s a subliminal message of sincerity that some language experts consider contrived.

Bill McGowan, a communications coach and chief executive of Clarity Media Group, calls the hand-on-heart motion “the gesture du jour.” He said he has noticed that other politicians have adopted the habit, and he doesn’t think it’s entirely artless.