I seem to be noticing it more and more recently: Musicians warming up onstage before a performance and playing signature bits of the piece they are about to perform. I don’t know if it’s happening more or, for some reason, I’m just aware of it more.

The other night took the cake though. Before a performance of Bartok’s “Music for Strings, Percussion, and Celesta,” the pianist, center stage, was hammering away on her big solos, very distinctive licks from the piece.

Back in my day — which admittedly was a long time ago — this kind of thing was frowned upon. We were told, or at least I was told, that you don’t play anything from the repertoire you are about to perform as you are warming up onstage. It was considered bad form.

For one thing, it gives the impression to the audience that the musician hasn’t mastered his or her part yet. It gives the impression that there haven’t been enough rehearsals. It gives the impression that the musician hasn’t practiced on his own. It may also suggest that the musician doesn’t give a damn.

Further, when a musician plays a bit of a piece before the performance, it’s a kind of spoiler. To the listener who doesn’t know the piece about to be performed, it may not matter much. But to the listener who does, it puts him ahead of things, as if he were viewing a key scene from a movie (Bergman pulling a gun on Bogart, say) before the movie runs.

For similar reasons, believe it or not, I don’t even like hearing snatches of pieces in pre-concert lectures. I’m probably in the minority on this one — it seems like most people consider concerts “learning experiences” these days — but to me it’s like tasting a dinner before it is served. I want to sit down and listen to a piece fresh, hear it in the order and context it was meant o be heard in, and not have bits of it brought to the attention of my ears beforehand like one of those Norton scores with the highlighted themes. That’s for school.

Musicians, if you think about it, are the only performers we regularly witness warming up. We never see, for instance, actors rehearsing their lines and movements on stage before a play. If we did, we wouldn’t like it. Why should it be any different with musicians?