They're sync indicators telling you that the clip has associated audio that's out of sync, and by how much.
jim, thanks for that. So should I take action by movimg either vid or audio back/forward to match ? It's hard to tell on the preview render as it's stuttering so much. I ask because, from your remark about switching them off in preferences, it seems like you're saying I can ignore them ??
Well, you're the editor. If the clips are good where they are, leave them be. If you want them moved so they're in sync, do so.